Evidence for crustal removal, tectonic erosion and flare-ups from the Japanese evolving forearc sediment provenance

Daniel Pastor-Galán , Christopher Spencer , Tan Furukawa, Tatsuki Tsujimori 

Forearc basins preserve the geologic record relating strictly to arc magmatism. The provenance of forearc sediment can be used to differentiate periods of crustal growth, accretion, and destruction, enhanced magmatism, advancing and retreating subduction slabs, delamination, etc. All these tectonic events systems predict differing degrees of sedimentary reworking of the older forearc units. Additionally, Hf isotopes of zircon can be used to evaluate the degree of continental reworking that occurs in the arc system. In this paper, we evaluate the changes in a long-lived subduction system using detrital zircon U-Pb and Hf data from forearc units in northern Honshu, Japan that span in age from the Silurian Period to the present from the forearc provenance of the Japanese subduction system. Our data demonstrate a series of dominant age peaks (430 ± 20, 360 ± 10, 270 ± 20, 184 ± 12, 112 ± 22, and 7 ± 7 Ma) and a progressive loss of the older zircon populations. Zircon Hf data reveal three discrete shifts that correspond to differing degrees of isotopic enrichment and correlate with changes in the dominant zircon age peaks. Additionally, each temporal isotopic shift is associated with isolation of the older sedimentary packages wherein no detrital zircon from the previous stages are observed in subsequent stages. We propose these shifts provide evidence for rapid shifts in arc tectonics including: magmatic flare-ups, producing the dominant peaks; protracted tectonic erosion progressively removing older sources of zircons reveals; a late Carboniferous event triggering the complete removal of the Precambrian crust; and the Cretaceous melting of the entire Permian arc crust, likely related with the subduction of the mid-oceanic ridge separating the Izanagi and Pacific plates.