5:15 PM - 6:45 PM
[MIS23-P11] Formation history of granitic batholith traced by multiple geochemical analysis of detrital zircon in the Permian-Early Cretaceous accretionary complex of the NE Japan
Keywords:detrital zircon, North Kitakami Belt, Nedamo Belt, U-Pb age
The eastern margin of the Asian continent, including Japanese islands, is characterized by the geological suites formed by the Pacific-type orogeny that has persisted since ca. 500 Ma. The geochemistry of the granitic batholiths in the orogenic system allows us to elucidate the inner material structure and tectonics in the subduction zone (Chapman et al., 2017). However, most of the pre-Jurassic granitoids in the eastern margin of the Asian continent are limited in their distribution possibly due to some geological removal processes, making it difficult to estimate the past tectonics. In this study, we focused on the detrital zircon geochemistry from the North Kitakami Belt (Late Permian-Early Cretaceous) and the Nedamo Belt (Late Permian-Early Triassic) to clarify the granitoid formation history and tectonics from the Permian to Jurassic.
The U–Pb ages of the detrital zircons from the Jurassic accretionary complexes show the bimodal distributions of the Late Permian to the Early Triassic and the Late Triassic to the Early Cretaceous in their histograms. Those from the Late Permian ones show the unimodal distributions of the Late Permian to the Early Triassic in the distributions. The 330-240 Ma zircons from the Late Permian accretionary complexes exhibit lower U/Yb ratios (0.1-0.7). In contrast, the 300-240 Ma zircons from the Jurassic accretionary complexes exhibit higher U/Yb ratios (0.7-2.0). Moreover, the 240-150 Ma zircons from the Jurassic ones also show higher U/Yb ratios (0.7-3.0). Based on the variations of their Hf concentrations and Eu anomalies, the temporal variation of the U/Yb ratios could be explained by the difference of the crustal-material geochemistry forming the magma rather than the difference of the magma differentiations. The plots of Hf vs. U/Yb show that the zircon compositions of the Late Permian accretionary complexes overlap with those from the immature magmas formed at the oceanic island arcs, while those of the Jurassic accretionary complexes overlap with those of the mature magmas formed at the continental arcs (Barth et al., 2017).
Based on these results, we conclude that 1) the Late Permian to Early Triassic granitic batholiths were distributed in the hinterland during the formation of the Late Permian accretionary complexes, and the Late Permian to Early Triassic and Late Triassic to Jurassic granitic ones were present during the formation of the Jurassic accretionary complexes, 2) the granitic batholiths that supplied the zircons to the Late Permian accretionary complexes were formed from the low-U/Yb immature crustal materials on the trench side, whereas the granitic batholiths suppling the zircons to the Jurassic accretionary complexes were formed from the high-U/Yb mature crustal materials in the continental interior. The changes in the source of the granitic materials to the continental margin from the Permian to Jurassic suggest that most of the immature Late Permian to Early Triassic granitic batholiths on the trench side were lost by some processes during the Permian to Jurassic.
The U–Pb ages of the detrital zircons from the Jurassic accretionary complexes show the bimodal distributions of the Late Permian to the Early Triassic and the Late Triassic to the Early Cretaceous in their histograms. Those from the Late Permian ones show the unimodal distributions of the Late Permian to the Early Triassic in the distributions. The 330-240 Ma zircons from the Late Permian accretionary complexes exhibit lower U/Yb ratios (0.1-0.7). In contrast, the 300-240 Ma zircons from the Jurassic accretionary complexes exhibit higher U/Yb ratios (0.7-2.0). Moreover, the 240-150 Ma zircons from the Jurassic ones also show higher U/Yb ratios (0.7-3.0). Based on the variations of their Hf concentrations and Eu anomalies, the temporal variation of the U/Yb ratios could be explained by the difference of the crustal-material geochemistry forming the magma rather than the difference of the magma differentiations. The plots of Hf vs. U/Yb show that the zircon compositions of the Late Permian accretionary complexes overlap with those from the immature magmas formed at the oceanic island arcs, while those of the Jurassic accretionary complexes overlap with those of the mature magmas formed at the continental arcs (Barth et al., 2017).
Based on these results, we conclude that 1) the Late Permian to Early Triassic granitic batholiths were distributed in the hinterland during the formation of the Late Permian accretionary complexes, and the Late Permian to Early Triassic and Late Triassic to Jurassic granitic ones were present during the formation of the Jurassic accretionary complexes, 2) the granitic batholiths that supplied the zircons to the Late Permian accretionary complexes were formed from the low-U/Yb immature crustal materials on the trench side, whereas the granitic batholiths suppling the zircons to the Jurassic accretionary complexes were formed from the high-U/Yb mature crustal materials in the continental interior. The changes in the source of the granitic materials to the continental margin from the Permian to Jurassic suggest that most of the immature Late Permian to Early Triassic granitic batholiths on the trench side were lost by some processes during the Permian to Jurassic.