Abstract
There was a hiatus in magmatism in Korea and Japan, located on the eastern continental margin of Asia, during a period of about 40 Ma from 160 Ma to 120 Ma. The cause of the resumption of magmatism since then is not yet well understood. In this study, we analyzed the Hf isotope composition of detrital zircons in the Cretaceous sediments of Korea (Hayang Group) and Japan (Goshoura and Himenoura groups) to investigate the tectonic evolution of eastern Asia in the Early Cretaceous period. εHf(t) in Cretaceous zircons from Japanese samples values from +8.2 to +0.1, suggesting that magmatism was sourced from the depleted juvenile materials, which is compatible with ridge subduction and subsequent melting of the young oceanic crust. εHf(t) values from Cretaceous zircons in the Hayang Group are negative, except for the Jindong Formation, which had a sediment supply from Japan, indicating that the old continental crust material of the Korean Peninsula was included in the magma generation. The detrital zircons of this study exhibit a depleted isotopic character at the beginning of subduction-related magmatism in Permian and Early Cretaceous, and then gradually change to a more enriched composition. This trend may be a typical example of the Pacific-type orogenic cycle.
Highlights
Introduction and General GeologyThe assembly of continental fragments in East Asia appears to have been completed during theEarly Triassic period, when there was a continental collision between North China and South China blocks [1,2]
Most of the detrital zircons separated from the sandstones of the Himenoura Group and the Goshoura Group of SW Japan except for one sample (Kuma-5) have crystal shapes of euhedral to subhedral with well-developed oscillatory growth zoning with no evidence of pre-Cretaceous zircon or old cores in CL images (Figure 2)
The detrital zircons with Paleoproterozoic ages indicate sediment supply from the inland area, possibly from the Korean Peninsula that was connected during their deposition
Summary
Introduction and General GeologyThe assembly of continental fragments in East Asia appears to have been completed during theEarly Triassic period, when there was a continental collision between North China and South China blocks [1,2]. The assembly of continental fragments in East Asia appears to have been completed during the. In the process of assembling continental fragments such as South China Block, North. China Block, and Japanese Islands in this region, the Paleo-Pacific plates to the east have subducted below them and have triggered various tectonic activities and tectono-magmatic processes, including subduction-related magmatism [3,4,5], metamorphism [6,7,8], and terrestrial basin formation [9,10,11]. In the eastern margin of the Eurasia continent, especially in Japanese islands, igneous activities related to subduction of the Paleo-Pacific plate are observed even long before its complete assembly.
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