講演情報
[T6-P-4]Pulsatile nature of the Ryoke granitoid intrusions in the central Mie prefecture (SW Japan) inferred by U-Pb zircon dating
*金 鐵祐1、河上 哲生1、東野 文子1、工藤 駿平1、中野 美玖、仁木 創太2、平田 岳史3 (1. 京都大学理学研究科地球惑星科学専攻、2. 名古屋大学宇宙地球環境研究所、3. 東京大学大学院理学系研究科地殻化学実験施設)
キーワード：
領家帯、花崗岩類、U-Pbジルコン年代測定、LA-ICP-MS
The Ryoke belt records the Cretaceous magmatic flare-up in East Asia and along arc variation of the magmatic pulses is studied in detail. Recently, U-Pb zircon ages of the granitoids accumulated in the Mikawa [1, 2] and Yanai [3] areas revealed a variation in pulsed magmatism within the Ryoke belt. Meanwhile, in the central Mie prefecture, such scheme is yet to be established despite several U-Pb zircon ages of the granitoids are reported [4, 5]. This study reports new U-Pb zircon ages of the Ryoke granitoids (nomenclature after [6]) of this area and compared its magmatic scheme with other regions of the Ryoke belt.
Weakly mylonitised Yokono granodiorite consists mainly of Qtz+Pl+Kfs+Bt. Zircon is present in the matrix or included in Pl and Kfs porphyroclasts. Weakly foliated Fukudayama granodiorite mainly consists of Qtz+Pl+Bt+Hbl, and zircon is found in the matrix and included in Pl and Bt. In both granitoids, CL-dark oscillatory-zoned domain is located in the outer part of zircon. The weighted mean U-Pb ages ±2σ error of these domains are 90±1 Ma for Yokono granodiorite, and 88±1 Ma for Fukudayama granodiorite. These are interpreted as magmatic ages since they are obtained from the oscillatory-zoned domain.
Compilation of the U-Pb zircon ages of the Ryoke granitoids from the central Mie prefecture [4, 5] and this study revealed three magmatic pulses at ca. 110-100 Ma, ca. 90 Ma, and ca. 80-70 Ma. The similarity of the magmatic scheme of this area and the Mikawa area is shown by the wide exposure of the youngest pulse plutons from the north to the vicinity of the MTL in the south. Meanwhile, the differences of the two areas are shown by the presence of ca. 90 Ma pulse and the older-aged nature of the oldest pulse in central Mie. The areal distribution of the oldest pulse plutons is also different. The ca. 110-100 Ma pulse plutons are widely exposed to the south of the Grt-Crd zone in central Mie, while ca. 99-95 Ma pulse plutons occur to the north of the Grt-Crd zone in Mikawa. Oscillatory-zoned ca. 100 Ma inherited cores from ca. 70 Ma granite [5] may imply that the ca. 110-100 Ma pulse plutons are wider-spread than currently exposed in central Mie.
References
[1] Takatsuka+ (2018a) Island Arc [2] Takatsuka+ (2018b) Lithos [3] Skrzypek+ (2016) Lithos [4] Higashino+ (2023) JAMS abstract [5] Kim+ (2024) JpGU abstract [6] Hayama+ (1982) J. Geol. Soc. Japan
Weakly mylonitised Yokono granodiorite consists mainly of Qtz+Pl+Kfs+Bt. Zircon is present in the matrix or included in Pl and Kfs porphyroclasts. Weakly foliated Fukudayama granodiorite mainly consists of Qtz+Pl+Bt+Hbl, and zircon is found in the matrix and included in Pl and Bt. In both granitoids, CL-dark oscillatory-zoned domain is located in the outer part of zircon. The weighted mean U-Pb ages ±2σ error of these domains are 90±1 Ma for Yokono granodiorite, and 88±1 Ma for Fukudayama granodiorite. These are interpreted as magmatic ages since they are obtained from the oscillatory-zoned domain.
Compilation of the U-Pb zircon ages of the Ryoke granitoids from the central Mie prefecture [4, 5] and this study revealed three magmatic pulses at ca. 110-100 Ma, ca. 90 Ma, and ca. 80-70 Ma. The similarity of the magmatic scheme of this area and the Mikawa area is shown by the wide exposure of the youngest pulse plutons from the north to the vicinity of the MTL in the south. Meanwhile, the differences of the two areas are shown by the presence of ca. 90 Ma pulse and the older-aged nature of the oldest pulse in central Mie. The areal distribution of the oldest pulse plutons is also different. The ca. 110-100 Ma pulse plutons are widely exposed to the south of the Grt-Crd zone in central Mie, while ca. 99-95 Ma pulse plutons occur to the north of the Grt-Crd zone in Mikawa. Oscillatory-zoned ca. 100 Ma inherited cores from ca. 70 Ma granite [5] may imply that the ca. 110-100 Ma pulse plutons are wider-spread than currently exposed in central Mie.
References
[1] Takatsuka+ (2018a) Island Arc [2] Takatsuka+ (2018b) Lithos [3] Skrzypek+ (2016) Lithos [4] Higashino+ (2023) JAMS abstract [5] Kim+ (2024) JpGU abstract [6] Hayama+ (1982) J. Geol. Soc. Japan
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