Repeated metamorphism in the pelitic granulites of the Hidaka metamorphic belt, Hokkaido, Japan: Implications for the formation of the present‐day trench‐arc‐basin system in NE Asia

Abstract

The timing and mechanism of the tectonic transition from an active continental margin to a trench‐arc‐basin system in NE Asia are debated. In this study, we report the pressure–temperature–time (P–T–t) path of this transition based on petrographic observations, phase‐equilibrium modelling, and U–Pb ages of zircon and rutile from pelitic granulites in the Hidaka metamorphic belt (Hokkaido, Japan). The granulites contain an early phase mineral assemblage of staurolite + sillimanite + biotite + plagioclase + quartz + rutile/ilmenite, a peak phase granulite assemblage of garnet + biotite + cordierite + plagioclase + quartz + rutile/ilmenite and a symplectic intergrowth of spinel + cordierite ± sillimanite within garnet porphyroblasts. Phase‐equilibrium modelling indicates two phases of metamorphism with P–T conditions, respectively, of ~6 kbar/620–670°C and ~6 kbar/850°C. A clockwise P–T path was thus reconstructed for the granulites, showing a near‐isobaric temperature increase to the peak conditions and a post‐peak cooling. U–Pb dating of zircon and rutile in the granulites yielded two groupings of metamorphic ages at c. 37 Ma and 19 Ma, related to early phase amphibolite facies and late phase granulite facies metamorphism, respectively. The age of magmatism from the previous work at the NE Asian continental margin overlaps with these metamorphic ages, and the two phases of metamorphism in the pelitic granulites is attributed to discrete episodes of supra‐subduction‐zone magmatism (late Eocene, c. 37 Ma) and back‐arc extension (early Miocene, 24–19 Ma). Consequently, we suggest that the Hidaka metamorphic belt has undergone two phases of metamorphism, which represent two pulsed and separated thermal events. Moreover, we relate the granulites facies metamorphism to the underplating of mafic magma and lithospheric thinning during the opening of the Japan Sea at 24–19 Ma, which is attributed to slab rollback and trench retreat processes in NE Asia.

Differential Uplift Triggered Basin‐And‐Range System: Evidence From Low‐Temperature Thermochronology in Eastern NE Asia

“…Recent investigations, including heat flow calculations, analysis of geomagnetic anomalies, and the study of granulite‐facies metamorphism from Hokkaido, Japan, have strongly suggested that the opening of the Japan Sea occurred approximately at 20 Ma (e.g., Lallemand & Jolivet, 1986; J. Zhang et al., 2022). The mechanism responsible for the Japan Sea opening is believed to result from the joint slab rollback of the PP and trench rollback (Xu et al., 2022).…”

Coupling Between Exhumation and Subduction: A Case Study From the Southern Great Xing'an Range, NE Asia

“…From the Miocene, continuous slab roll‐back of the Pacific Ocean and retreat of the trench (Xu et al., 2022) triggered extensive back‐arc extension on the NE Asian continental margin (Xu et al., 2022) which caused the opening of the Sea of Japan (ca. 24–19 Ma, Tang et al., 2016; J. Zhang et al., 2022), exhumation on the NE Asian continental margin (ca. 23 Ma, Y. P. Zhang et al., 2022) and the GXR (ca.…”