Petrogenesis of the Kaikomagatake granitoid pluton in the Izu Collision Zone, central Japan: implications for transformation of juvenile oceanic arc into mature continental crust |
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| Authors: | Satoshi Saito Makoto Arima Takashi Nakajima Kenichiro Tani Takashi Miyazaki Ryoko Senda Qing Chang Toshiro Takahashi Yuka Hirahara and Jun-Ichi Kimura |
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| Institution: | (1) Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-Cho, Yokosuka, Kanagawa 237-0061, Japan;(2) Geological Institute, Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan;(3) Geological Museum, Geological Survey of Japan, AIST Central-7, 1-1-1 Higashi, Tsukuba 305-8567, Japan;(4) Present address: Research Institute for Humanity and Nature, 457-4 Motoyama, Kamigamo, Kita-ku, Kyoto 603-8047, Japan |
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| Abstract: | The Miocene Kaikomagatake pluton is one of the Neogene granitoid plutons exposed in the Izu Collision Zone, which is where
the juvenile Izu-Bonin oceanic arc is colliding against the mature Honshu arc. The pluton intrudes into the Cretaceous to
Paleogene Shimanto accretionary complex of the Honshu arc along the Itoigawa-Shizuoka Tectonic Line, which is the collisional
boundary between the two arcs. The pluton consists of hornblende–biotite granodiorite and biotite monzogranite, and has SiO2 contents of 68–75 wt%. It has high-K series compositions, and its incompatible element abundances are comparable to the average
upper continental crust. Major and trace element compositions of the pluton show well-defined chemical trends. The trends
can be interpreted with a crystal fractionation model involving the removal of plagioclase, biotite, hornblende, quartz, apatite,
and zircon from a potential parent magma with a composition of ~68 wt% SiO2. The Sr isotopic compositions, together with the partial melting modeling results, suggest that the parent magma is derived
by ~53% melting of a hybrid lower crustal source comprising ~30% Shimanto metasedimentary rocks of the Honshu arc and ~70%
K-enriched basaltic rocks of the Izu-Bonin rear-arc region. Together with previous studies on the Izu Collision Zone granitoid
plutons, the results of this study suggest that the chemical diversity within the parental magmas of the granitoid plutons
reflects the chemical variation of basaltic sources (i.e., across-arc chemical variation in the Izu-Bonin arc), as well as
a variable contribution of the metasedimentary component in the lower crustal source regions. In addition, the petrogenetic
models of the Izu Collision Zone granitoid plutons collectively suggest that the contribution of the metasedimentary component
is required to produce granitoid magma with compositions comparable to the average upper continental crust. The Izu Collision
Zone plutons provide an exceptional example of the transformation of a juvenile oceanic arc into mature continental crust. |
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