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[MGI34-P01] Present situations and challenges in understanding the geochemical characteristics of the Japan arc, as shown by the area ratio and the geochemical data of each lithological groups.
Keywords:geochemical database, Seamless Geologigal Map, category of lithology, geochemical characteristics of Japan arc
Many studies for the area ratio of geological components of the Japan arc have been published according to the trends of geological research in each era since the geological map of the Japan was completed. Studies of development of geological structures in the Japan arc from geochemical approaches have also been promoted, reflecting trends in chemical analysis in each era and the construction and revision of geological development models. The studies of the geochemical development process of the Japan arc based on these researches is still an ongoing research subject.
Haraguchi et al. (2020 JpGU) discussed the “east-west difference” of each lithology of the crust components of the Japan arc based on the compiled data by the geochemical database “DODAI (Haraguchi et al., 2018)”. From the comparison between the compiled data and the exposed area ratio based on the “Seamless Digital Geological Map of Japan” by Geological Survey of Japan, it was revealed that the number of chemical data differs greatly for each lithology.
In the Seamless Geological Map, the basic lithological groups are divided into “igneous rocks”, “sedimentary rocks”, “metamorphic rocks”, and “accretionary prism”, has been set up with the progress of research on accretionary prisms since the 1980s. Because “accretionary prism” is a classification based on tectonics, many of the individual studies use the conventional lithological classification of “igneous”, “sedimentary”, and “metamorphic” even in the accretionary prism geology.
According to the data compiled by DODAI, the number of plutonic rock data is about 37% of the total, which is higher than the area ratio of about 11% on the Seamless Geological Map, indicating that plutonic rocks are attracting a lot of attention from the geochemical studies. On the other hand, metamorphic rocks have an area ratio of about 19% including accretionary prisms, while DODAI recording data is as small as about 8%, suggesting that it is a difficult to approach from the geochemical researches. In addition, extremely small number or difficult to belong chemical data in detailed lithological groups, such as “sandstone” and “mudstone” in “sedimentary”, occur depending on the method of division. The geological unit “conglomerate”, “alternation of sand and mud”, and “mixed rock (melange)” are difficult to relate from the chemistry because geochemical studies of these components are mainly in individual components of each groups. These are issues in considering the each lithologies and average composition of the Japan arc crust. In this report, we would like to introduce the current situations and issues in considering the geochemical characteristics of the Japan arc based on the characteristics of these geological and geochemical data.
Acknowledgments
We would like to thank Mr. Yoshiharu Nishioka (AIST) for his cooperation in calculating the area ratio for each lithology based on the Seamless Geological Map.
Haraguchi et al. (2020 JpGU) discussed the “east-west difference” of each lithology of the crust components of the Japan arc based on the compiled data by the geochemical database “DODAI (Haraguchi et al., 2018)”. From the comparison between the compiled data and the exposed area ratio based on the “Seamless Digital Geological Map of Japan” by Geological Survey of Japan, it was revealed that the number of chemical data differs greatly for each lithology.
In the Seamless Geological Map, the basic lithological groups are divided into “igneous rocks”, “sedimentary rocks”, “metamorphic rocks”, and “accretionary prism”, has been set up with the progress of research on accretionary prisms since the 1980s. Because “accretionary prism” is a classification based on tectonics, many of the individual studies use the conventional lithological classification of “igneous”, “sedimentary”, and “metamorphic” even in the accretionary prism geology.
According to the data compiled by DODAI, the number of plutonic rock data is about 37% of the total, which is higher than the area ratio of about 11% on the Seamless Geological Map, indicating that plutonic rocks are attracting a lot of attention from the geochemical studies. On the other hand, metamorphic rocks have an area ratio of about 19% including accretionary prisms, while DODAI recording data is as small as about 8%, suggesting that it is a difficult to approach from the geochemical researches. In addition, extremely small number or difficult to belong chemical data in detailed lithological groups, such as “sandstone” and “mudstone” in “sedimentary”, occur depending on the method of division. The geological unit “conglomerate”, “alternation of sand and mud”, and “mixed rock (melange)” are difficult to relate from the chemistry because geochemical studies of these components are mainly in individual components of each groups. These are issues in considering the each lithologies and average composition of the Japan arc crust. In this report, we would like to introduce the current situations and issues in considering the geochemical characteristics of the Japan arc based on the characteristics of these geological and geochemical data.
Acknowledgments
We would like to thank Mr. Yoshiharu Nishioka (AIST) for his cooperation in calculating the area ratio for each lithology based on the Seamless Geological Map.