Ocean Drilling Program (ODP) Leg 190 was concerned with coring and sampling five sites (Sites 1173-1176 and 1178) along the Muroto Transect across the Nankai Trough accretionary prism (Fig. F1) (Moore, Taira, Klaus, et al., 2001; Moore et al., 2001). The Muroto Transect is southeast of Cape Muroto in southwest Japan and includes ODP Site 808 (Leg 131). An additional site was drilled to the west (Site 1177) that, along with some Deep Sea Drilling Project (DSDP) sites (Leg 87, Sites 582 and 583), provided a second transect (the Ashizuri Transect) (Fig. F1). The main objectives of Leg 190 were to (1) examine the structure of the Nankai Trough accretionary prism and find its relationship to diagenesis and fluids and (2) provide constraints on the contrasting stratigraphic and structural development of the accretionary prism along strike. Previous workers (De Rosa et al., 1986; Taira and Niitsuma, 1986; Marsaglia et al., 1992; Underwood et al., 1993) have shown that sands in the Nankai Trough were derived from several main sources since the Pliocene and are a reflection of the complex tectonics of the region including uplift of the Shimanto subduction complex on Shikoku and island arc collision in central Honshu.
This paper concerns sand composition and provenance from all Leg 190 sites and complements previous studies of Nankai Trough sands. The main aim is to document framework detrital modes of sand/sandstone sampled during Leg 190 deep-sea drilling for the first time including a Pliocene-Pleistocene lower trench-slope basin, late Miocene accreted trench fill of the Nankai Trough accretionary prism, and Miocene turbidite facies of the Shikoku Basin succession. Three sand petrofacies are recognized (volcaniclastic, quartzose, and sedimenticlastic), and these demonstrate the wide variations in sand compositions that can be encountered in a subduction zone setting. Tentative conclusions about the provenance of Leg 190 sands also provide some constraints on the sediment dispersal pattern in a subduction zone setting, namely, the role of transverse delivery of sands down the trench-slope as opposed to longitudinal sand supply along the trench (e.g., Dickinson, 1982).