Jurassic synorogenic basin filling in western Korea: sedimentary response to inception of the western Circum‐Pacific orogeny

Abstract

This is the first sedimentologic and stratigraphic attempt to demonstrate Jurassic subduction‐induced basin‐filling processes in the early stage of the western Circum‐Pacific orogeny. The Chungnam Basin in western Korea was filled with a Lower to Middle Jurassic nonmarine succession, the Nampo Group, whose deposition postdated the Triassic final assembly of Chinese continental blocks. The Nampo Group consists of two repeated, fining‐ to coarsening‐upward alluvio‐lacustrine sequences, separated by an interval of thick breccia–gravel progradation deposits and its related strong proximal unconformities. No temporal variation in the degree of chemical weathering, along with the predominance of coals and a tropic to subtropic paleoflora, reveals little or no climate fluctuations during deposition of the Nampo Group. The observed relationships provide a record of sedimentation most likely controlled by temporal variations of tectonically driven sediment flux. Such syntectonic sedimentation of the Chungnam Basin occurred at a convergent margin of continental‐arc setting during the Daebo orogeny, synchronous with the early subduction of the western paleo‐Pacific ocean that resulted in formation of an accretionary complex along the East Asian continental margin during Jurassic time. Hence, synorogenic deposition in the Chungnam Basin is interpreted as sedimentary response to subduction–accretion of the western paleo‐Pacific plate.

Detrital record of mountain building: Provenance of Jurassic foreland basin to the Dabie Mountains

“…Sedimentary basins occupying an analogous tectonic position to the Huangshi foreland basin lie to the south of these collisional belts and all contain Early to Middle Jurassic sedimentary infill. In Korea this succession is represented by the Nampo Group and equivalent strata [ Jeon et al , 2007; Egawa and Lee , 2009] and in Japan by the Kamiaso turbidites in the Mino terrane (Figure 10) [ Isozaki , 1997; Hidaka et al , 2002; Nutman et al , 2006; Tsujimori et al , 2006]. Detrital zircon data from these Korean and Japanese successions are similar to the Huangshi strata and include a major component of late Paleoproterozoic detritus (Figures 12h and 12i) likely derived from the South China Craton and Phanerozoic debris from the exhumed collisional belt.…”

East Asia-Wide Flat Slab Subduction and Jurassic Synorogenic Basin Evolution in West Korea

“…The interplay between oceanic plate subduction and the development of continental margins is of considerable geological interest, and of a particular interest for Asian structural geologists and petrologists is the subduction of the present and ancient Pacific plates, which triggered orogenic development and contributed to crustal evolution in the circum-Pacific regions through the Phanerozoic [1,2]. Since the Triassic, the northwestern circum-Pacific region (also known as the East Asian continental margin) initiated the evolution of a continental arc stretching several thousand kilometers, which resulted in an East Asia-wide crustal shortening and thickening, orogenic basin formation, and landward magmatic progradation [2,3,4,5,6,7,8,9]. It is noted that although the paleo-Pacific subduction along this region was also present in Paleozoic time, it did not exert a major tectonic impact on the Asian continents [10,11,12], and that this lack of impact was probably related to the fact that the Paleotethys Ocean lay between Laurasia and Gondwana until the Triassic period when the East Asian continental blocks had not been yet assembled [13,14].…”

K-Ar dating of illites for time constraint on tectonic burial metamorphism of the Jurassic Nampo Group (West Korea)

“…This study deals with K-Ar illite dating of the Nampo Group, a Lower to Middle Jurassic nonmarine basin-fill of the Chungnam Basin located in the central western Korean Peninsula (Fig. 1a) (Egawa and Lee, 2009 and references therein), to infer the age of diagenesis or low-grade metamorphism induced by postdepositional crustal loading. The Nampo Group in the Ocheon area comprises the Hajo, Amisan, Jogyeri, and Baegunsan formations with decreasing age and is structurally overlain by pre-Jurassic basement rocks (Choi et al, 1987;Lee, 2006, 2008).…”