日本地球惑星科学連合2018年大会

講演情報

[JJ] ポスター発表

セッション記号 S (固体地球科学) » S-GL 地質学

[S-GL30] 地球年代学・同位体地球科学

2018年5月23日(水) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:田上 高広(京都大学大学院理学研究科)、佐野 有司(東京大学大気海洋研究所海洋地球システム研究系)

[SGL30-P01] Spatiotemporal evolution of magmatic pulses and regional metamorphism during a Cretaceous flare-up event: constraints from the Ryoke belt (Mikawa area, central Japan)

★Invited Papers

*河上 哲生1高塚 紘太1Skrzypek Etienne1坂田 周平1,2大林 秀行1平田 岳史1,3 (1.京都大学大学院理学研究科、2.学習院大学、3.東京大学)

キーワード:U-Pbジルコン年代測定、フレア・アップ、低圧高温型変成作用、花崗岩、大陸地殻の形成

The spatiotemporal relationship between granitoid intrusions and low-P/T type regional metamorphism in the Ryoke belt (Mikawa area, central Japan) is investigated to understand the evolution of the upper- to middle-crust during the Cretaceous flare-up event at the active Eurasian continental margin. Following three stages are recognized; (1) 99−84 Ma: the gneissose granitoid intrusions of the 99 Ma pulse (ca. 99-95 Ma) into the shallow crust and high-T regional metamorphism of the sillimanite-grade (97.0 ± 4.4 Ma to 88.5 ± 2.5 Ma) at the middle crust, (2) 81−75 Ma: the gneissose granitoid intrusions of the 80 Ma pulse into the middle crust, and (3) the voluminous massive to weakly-foliated granitoid intrusions of the 70 Ma pulse into ~9−12 km depths accompanied by contact metamorphic aureoles. Cooling of the metamorphic belt started at the final stage of (1). Between (2) and (3), entire regional metamorphic belt should be inclined to the north and exhumed to the depths of ~9−12 km. In spite of the temporal association, lack of spatial association between the highest-grade metamorphic zone and pre- to syn-metamorphic felsic plutons support transient thermal anomaly in the mantle and resulting heat conduction in the crust as a possible mechanism for the regional metamorphism. The successive emplacement of granitoids to shallow, deep and shallow levels of the crust is probably controlled by the thermal structure of the crust at each stage. The voluminous granitic continental crust formation and intrusion into the shallow levels of the crust at ca. 99−70 Ma in the Mikawa area probably reflects drastic and significant thermal/material input from the mantle at the active continental margin.