Provenance of Jurassic accretionary complex: Mino terrane, inner zone of south‐west Japan – implications for palaeogeography of eastern Asia

Abstract

Provenance and tectonic history of the Jurassic accretionary complex, Mino terrane, located in the Inner Zone of south-west Japan, were studied using sandstone framework composition and mudrock geochemistry. Modal analysis of sandstones shows that the tectonic setting of the source area for the studied Mino terrane clastic rocks was uplifted basement, largely dominated by highgrade metamorphic terrain composed of quartz and feldspar, especially plagioclase. The textural and mineralogical immaturity, extent of alkali and alkaline earth element leaching, low chemical index of alteration values and depleted rare earth element (REE) contents suggest rapid uplift and erosion within the source terrain and a relatively weak weathering intensity. Factor analysis revealed that grain-size effects governed compositional heterogeneity in the studied sediments. Provenance of the sediments is interpreted as being plagioclase-enriched felsic basement rock, such as granodiorite, within a continental margin and evolved arc tectonic setting rather than active volcanic arc. Lack of a contribution from active volcanic arcs may have resulted from the cessation of volcanism during the reorganization of the subducting plate system and/or erosion of arc volcanics and exposure of basement. Considering the previous studies on palaeogeography and palaeocurrent reconstruction, the north-eastern part of the Yeongnam massif in the Korean Peninsula is interpreted as the most probable source area for the studied turbidites. The results of mixing calculation for Mino terrane sediments suggest that Precambrian leucocratic granite and the basement rock of the Cretaceous Gyeongsang Basin shed large amounts of sediments to the Mino trench, whilst Precambrian granitic gneiss and the Triassic pluton supplied lesser amounts. The results of this study reveal that, although active subduction-accretion processes were occurring, the Mino trench was bordered by continental basement rocks. This knowledge contributes to enhanced understanding of the Jurassic palaeogeography of the east Asia continental margin.

Geochemistry of shales of the Upper Cretaceous Hayang Group, SE Korea: Implications for provenance and source weathering at an active continental margin

“…= 69) shales may reflect recycling, considering that much of these sediments were derived from the Jurassic Mino accretionary complex (terrane) in SW Japan (Chang et al, 1990;Kamata et al, 2000;Mitsugi et al, 2001;Lee and Kim, 2005). Joo et al (2007) described the geochemistry of the Jurassic Mino terrane sediments, and showed that Mino terrane sands and muds exhibit a dispersed trend in A-CN-K space, from granodiorite source towards illite (CIA: 44-78) indicative of non-steady state weathering conditions in the source area. This interpretation suggests that recycling was a significant process during deposition of the Donghwachi and Gisadong shales, and that recycling of fine-grained rocks may mask the weathering history of the source terrain.…”

“…EM 1: Precambrian gneissic-granitic rock (Hong, 1992); EM 2: Triassic Yeongdeok Granite (Kim, 2002); EM 3: average clastic rocks of the Mino accretionary complex, SW Japan (Joo et al, 2007); EM 4: Triassic chert of the Mino accretionary complex, SW Japan (Shimizu et al, 2001); EM 5: Chaeyaksan basaltic rock (Kim et al, 1999).…”

“…b Triassic Yeongdeok Granite (Kim, 2002). c Mino terrane clastic rocks, SW Japan (Joo et al, 2007). d Mino terrane chert, SW Japan (Shimizu et al, 2001).…”

“…EM 2 is the Triassic Yeongdeok Granite located in the central part of the study area (Kim, 2002). EM 3 represents the average composition of clastic rocks in the chert-clastic sequence in the Mino accretionary complex, SW Japan (Joo et al, 2007), while EM 4 is the average composition of Triassic chert from the same complex (Shimizu et al, 2001). Clastic and chert end members derived from the Mino complex were treated separately.…”

Paleogeographic reconstructions of the East Asia continental margin during the middle to late Mesozoic

“…1980; Kimura & Hori 1993) and is composed of turbidite sandstone–shale successions. Joo et al. (2007) studied turbidite sandstones and revealed that more than 55% of the framework grains in the sandstones are feldspar, followed by about 30% quartz.…”