Zircon and apatite thermochronology of the Nankai Trough accretionary prism and trench, Japan: Sediment transport in an active and collisional margin setting

Abstract

The Nankai accretionary complex is the most recent addition to the accretionary complexes of southwest Japan and has preserved a record of sediment flux to the trench during its construction. In this study, we use U‐Pb zircon and fission track analysis of both zircons and apatites from sediments taken from the forearc and trench of the Nankai Trough, as well as rivers from southwest Japan to examine the exhumation history of the margin since the Middle Miocene. Modern rivers show a flux dominated by erosion of the Mesozoic‐Eocene Shimanto and Sanbagawa accretionary complexes. Only the Fuji River, draining the collision zone between the Izu and Honshu arcs, is unique in showing much faster exhumation. Sediment from the Izu‐Honshu collision is not found 350–500 km along the margin offshore Kyushu indicating limited along‐strike sediment transport. Sediment deposited since 2 Ma on the midtrench slope offshore the Muroto Peninsula of Shikoku (ODP Site 1176) and on the lower slope trenchward of the Kumano Basin (IODP Sites C0006E and C00007E) shares the dominant source in the Shimanto and Sanbagawa complexes seen in the modern rivers. Prior to 5 Ma, additional sediment was being sourced from further north in more slowly exhumed terrains, ~350 km from the trench axis. Around 9.4 Ma, U‐Pb zircon ages of ~1800 Ma indicate enhanced erosion from the North China Craton, exposed in northern Honshu. In the middle Miocene, at ~15.4 Ma, the sediment was being derived from a much wider area including the Yangtze Craton (U‐Pb ages ~800 Ma). We suggest that this enhanced catchment may have reflected the influence of the Yangtze River in supplying into the Shikoku Basin prior to rifting of the Okinawa Trough at 10 Ma and migration of the Palau‐Kyushu Ridge to form a barrier to transport. The restriction of Nankai Trough provenance to Mesozoic source partly reflects continued uplift of the Shimanto and Sanbagawa complexes since the Middle Miocene.

Sediment flow routing during formation of forearc basins: Constraints from integrated analysis of detrital pyroxenes and stratigraphy in the Kumano Basin, Japan

“…This approach assumes limited compositional variation of source areas and no significant changes in on-land erosional and transport processes in the past 2.5 Ma. This assumption is in good agreement with broadly constant exhumation rates across the studied area and magmatic quiescence in SW Honshu during this period (Kimura et al, 2005;Clift et al, 2013).…”

“…In contrast, approaches using single grain geochemical analysis or single grain geochronology are not affected by alteration, hydrodynamic and diagenetic effects and, thus, allow a more robust and detailed characterisation of provenance (von Eynatten and Dunkl, 2012). In the Nankai margin, geochronology of detrital zircons can be used to determine the relative contribution of the Inner, Outer and Collision Zones in turbidites (Clift et al, 2013). This approach notably allowed assessment of clastic flux to the Nankai Trough in SW Japan over the past 14 m.y.…”

“…Similarly, igneous, metamorphic and sedimentary fragments reworked from the Inner and Outer Zones have been significant components of turbidites in the lower forearc (i.e., trench slope, trench-slope basins and trench) since the Miocene (De Rosa et al, 1986;Fergusson, 2003;Underwood et al, 2003;Underwood and Fergusson, 2005;Underwood and Moore, 2012;Clift et al, 2013;Usman et al, 2014). However, to date, constraints on the provenance of turbidites have been restricted to the modal composition of sandstones (e.g., Fergusson, 2003;Usman et al, 2014) and one zircon study (Clift et al, 2013). Although there is evidence that the morphology of the trench slope controlled distribution of turbidites during the Neogene (e.g., Underwood et al, 2003), patterns of detrital sedimentation associated with formation of the forearc basin remain to be determined.…”

The abanico plot: Visualising chronometric data with individual standard errors

“…4, p. 204. Such aligned plots have been already adopted by fission track dating groups (e.g., Clift et al 2013). However, a comprehensive view on both, standard error and data distribution characteristics requires further steps.…”

Gas-In-Place Estimate for Potential Gas Hydrate Concentrated Zone in the Kumano Basin, Nankai Trough Forearc, Japan

“…There have been significant fluctuations of sediment provenance and shifts in delivery pathways and rerouting since the basin's initiation [35][36][37][38]. A margin-wide assessment has shown that the submarine fans have transformed over time from a braided channel-dominated system to a small fan dominated system with shrinking, separated, small basins; to a trough fill turbidite system; to a channel-levee system [39][40][41].…”