2:45 PM - 3:00 PM
[SCG44-05] Petrogenetic study on the cretaceous granitoids on the Takanawa Peninsula, northwest Shikoku, southwest Japan
Keywords:Cretaceous Granitoids, Petrogenetic study, Flare-ups, Takanawa Peninsula
In recent years, felsic igneous activity during magmatic anomalies in volcanic arcs has attracted much attention as a key to understanding the formation and growth processes of continental crust. This period of anomalous magma generation is called "flare-up" (e.g., Paterson and Ducea, 2015), and is recognized on a global scale, from North and South America to the Pacific Rim of Eurasia.
Takanawa Peninsula in northwestern Shikoku is composed of plutonic rocks and related rocks including granitoids, mafic rocks, metamorphic rocks formed druing the Cretaceous flare-up event. The granitoids, which are the most widely exposed in the area, consist of several granitoid plutons with different petrological characteristics such as occurrence, mineral constituents and mineral modal ratio. The mantle-derived mafic rocks and metamorphic rocks of accretionary complex are distributed in the area, making the Takanawa Peninsula the best field to investigate thermal and chemical effects of mantle activity on the crust during the flare-ups. However, although wide range of studies including petrological studies by Ochi (1982), isotopic studies by Kagami et al. (1985; 1988), and geochronological studies by Yoshikura et al. (2004) and Shimooka et al. (2019) have been reported, no comprehensive petrogenetic studies on the granitoids have been conducted to elucidate the magmatic processes during the flare-ups in the Takanawa Peninsula.
In this study, I obtained new data including whole-rock and mineral chemical compositions, zircon U-Pb ages and Sr-Nd isotope ratios for the granitoids and related rocks to investigate the magma process of granitoids in the Takanawa Peninsula.
The results suggest that the granitoids in the Takanawa peninsula were formed from multiple pulsed magmas generated by partial melting of the mafic lower crust in 99 Ma, 96-93 Ma, and 89 Ma, which intruded, emplaced, and solidified in the middle crust. Based on the isotopic compositions, assimilation of the host metasedimentary rocks into the granitoid magmas is limited. The differences in the chemical compositions observed in the granitoid plutons are attributed to the degree of partial melting of the mafic lower crust and/or the degree of fractional crystallization of evolving magmas.
Takanawa Peninsula in northwestern Shikoku is composed of plutonic rocks and related rocks including granitoids, mafic rocks, metamorphic rocks formed druing the Cretaceous flare-up event. The granitoids, which are the most widely exposed in the area, consist of several granitoid plutons with different petrological characteristics such as occurrence, mineral constituents and mineral modal ratio. The mantle-derived mafic rocks and metamorphic rocks of accretionary complex are distributed in the area, making the Takanawa Peninsula the best field to investigate thermal and chemical effects of mantle activity on the crust during the flare-ups. However, although wide range of studies including petrological studies by Ochi (1982), isotopic studies by Kagami et al. (1985; 1988), and geochronological studies by Yoshikura et al. (2004) and Shimooka et al. (2019) have been reported, no comprehensive petrogenetic studies on the granitoids have been conducted to elucidate the magmatic processes during the flare-ups in the Takanawa Peninsula.
In this study, I obtained new data including whole-rock and mineral chemical compositions, zircon U-Pb ages and Sr-Nd isotope ratios for the granitoids and related rocks to investigate the magma process of granitoids in the Takanawa Peninsula.
The results suggest that the granitoids in the Takanawa peninsula were formed from multiple pulsed magmas generated by partial melting of the mafic lower crust in 99 Ma, 96-93 Ma, and 89 Ma, which intruded, emplaced, and solidified in the middle crust. Based on the isotopic compositions, assimilation of the host metasedimentary rocks into the granitoid magmas is limited. The differences in the chemical compositions observed in the granitoid plutons are attributed to the degree of partial melting of the mafic lower crust and/or the degree of fractional crystallization of evolving magmas.