Tectonic evolution of the Japanese islands as reflected in modal compositions of Cenozoic forearc and backarc sand and sandstone

Cenozoic tectonic evolution of the Japanese rifted continental arc‐trench system is reflected in the detrital modes of sand and sandstone deposited in forearc and backarc basins sampled by the Deep Sea Drilling Project. At present, the Japan arc is divided into two segments along a complex plate boundary where the Izu‐Bonin Ridge intersects the Japan arc, creating two triple junctions, in front of and behind the ridge. Southwest of the Izu‐Bonin Ridge, quartzofeldspathic Cretaceous forearc sediments were uplifted and recycled into Tertiary forearc deposits in response to strike‐slip movement associated with backarc spreading in the Shikoku basin. Quaternary forearc sections record the first major influx of volcanic detritus to southwest Japan sites. Triple‐junction‐related deformation in central Honshu has produced sand of mixed volcanic/sedimentary provenance, which is funneled by the Suruga Canyon into the Nankai Trough along the southwest Japan margin. North of the triple junction, Oligo‐Miocene forearc sand compositions indicate Oligocene forearc uplift and volcanism, possibly related to initial backarc rifting and formation of the Japan Sea, and subsequent Miocene exposure of arc basement. In contrast, Pliocene and Quaternary forearc sand from northeast Japan is primarily volcaniclastic and documents uninterrupted arc volcanism. Within the backarc region, sand compositions vary from east to west across the Japan Sea. The Asian rifted continental margin and submerged remnants shed quartzofeldspathic sand into the western side of the basin, whereas the Japan arc sheds volcaniclastic sand into the eastern side of the basin.