Intraplate-basaltic volcanism was widespread throughout Southeast (SE) Asia during the Cenozoic (Figure 1; Flower et al., 1998). Vietnam is located at the southeastern edge of SE Asia (Figure 1a) and represents the most volcanically active field on the Indochina Peninsula (Figure 1b; Flower et al., 1998). The upwelling of hot asthenospheric materials, revealed by seismic tomography (Huang et al., 2015), is considered to be a primary cause of the volcanism in this region.Lithospheric thinning, induced by the collision of the Indo-Australian plate and Eurasian plate, has long been proposed as a cause of asthenospheric upwelling (

552 grain size samples and 33 mineral quality defined samples have been collected in the Co To island, Tonkin Bay of Vietnam, to study the distribution and the sediment provenance. The field investigation method, the grain analysis, and the detrital composition examination method have been used to study the characteristics of the surface sediments in Co To island. The obtained results show that the surface sediments in the area consist of ten different fields, namely: sandy gravel, gravelly sand, sand, gravelly muddy sand, sand mixed gravel, muddy sand, gravelly mud mixed sand, silty sand, muddy sandy gravel, and sandy mud. The mineral component method shows that quartz is the main contain of the surface sediment (72,0÷90,6%), less rock detritus, felspat, mica, and very few of the shells. It is to confirm that the continent is the main primary material source of the study area. The distribution of the sediment is complicated. As the East-Southeast side of the research area, the sediment distribution following gravity way, coarse grain near the shore (gravel, sandy gravel,…), finer grain far off the shore (gravelly muddy sand, silty sand,…), choice level is very low. Which This is saying that the movement of sediment in the area is dominant, ; the flow energy is governed by the topography near the island and seafloor. In tMhe meanwhile, the west-northwest side, the topography of seafloor is the complicated, coarse sediment grains (gravel, sand), ); the roundness is bad, which is saying that the hydrodynamic flow there plays an important role in the sediment distribution.

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