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Chemical characteristics of biotites and hornblendes of Late Mesozoic to Early Tertiary granitic rocks in Japan

Satoshi Kanisawa
Satoshi Kanisawa
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January 01, 1983

Granites carrying magnetite, such as those in the Kitakami, Abukuma, and San-in—Shirakawa zones, have Mg-rich and Al-poor biotite and hornblende, whereas granites carrying ilmenite instead of magnetite, such as those of the Ryoke, Sanyo— Naegi zones, have Fe- and Al-rich ones. These differences of chemistry are conspicuous and reflect the oxygen fugacities during crystallization. Trace elements and fluorine content in the Kitakami and the Ryoke granites are also presented. In the Kitakami, Abukuma, and San-in granites, fluorine is distinctly concentrated into biotite and hornblende in the late stages of crystallization, but in some Ryoke granites, the relation between fluorine content and differentiation is indistinct. The granites in the former districts may have been closed with respect to fluorine, while those in the latter may have been open, and fluorine in the granitic magma is thought to have reacted to some degree with the surrounding rocks.

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GSA Memoirs

Circum-Pacific Plutonic Terranes

J. A. Roddick
J. A. Roddick
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Geological Society of America
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Publication date:
January 01, 1983




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