[MGI39-P03] Geochemical characteristics of Japan Arc basements from the geochemical database, and origin of these characteristics
Keywords:geochemical database, composition of Japanese arc crust, comparison between NE and SW Japan, statistics
As the Japan Arc crust is formed through complicated evolution until Paleozoic, for example, acidic plutons such as Hida and Ryoke granitoids produced by multiple activities after Paleozoic are distributed, accretion prisms are observed in SW Japan and Hokkaido arc, and the addition of arc crust occurs at the Izu collision zone. As such, geochemical discussion based on regionality is required to discuss a growth process of the earth crust.
As a database to use for this study, the data of the lithofacies to be related to the Japan Arc crust (basement) is extracted from the DODAI database. DODAI (Haraguchi et al., 2018) is a geochemical database for the basement rocks of the Japanese islands including major and trace element concentrations, isotopic ratios and geographical coordinates (latitude, longitude, and altitude) of sampling points, and geological and lithological information. This dataset is sorted by lithofacies and locations, and geochemical variations between lithofacies and locations are compared. For locality, we subdivided our dataset to Northeast (NE) and Southwest (SW) Japan divided at the Itoigawa - Shizuoka tectonic line. For lithological classification, a definition in Takeuchi et al. (2019) is used. We construct compositional histogram of each major and trace elements of each group. Based on the histogram, we calculate various statistics, average, median, mode, variance, skewness and kurtosis, and compare these plots and parameters.
when comparing the same lithological type between NE and SW Japan, many elements show different characteristics. Rocks of SW Japan typically show more evolved characteristics. On the other hand, rocks of NE Japan show low K2O, Rb and HREE, and high CaO and Sr. These statics also show more differentiated characteristics in SW Japan. In terms of statistical variables, rocks of SW Japan show larger variance and skewness, and lower kurtosis. In this report, we examine regionality of the compositional characteristics of Japan Arc crust from these data comparisons, and discuss a genetic process of the Japan arc.
Haraguchi et al. (2018) J. Geol. Soc. Japan 124, 1049-1054
Takeuchi et al. (2019) Phys. Earth Planet. Inter. 288, 37-57