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Study of sediment sources and transport pathways in the Chukchi and East Siberian Seas is vital for understanding the interaction of fluvial, ocean, and sea-ice dynamics. In this study, 42 samples were analyzed for heavy minerals and 23 were analyzed for garnet geochemistry. These analyses suggest that the surface sediment is mainly sourced from the surrounding rivers. There are distinctive performances between the heavy minerals and garnet geochemistry of sediments in the Chukchi Sea and the East Siberian Sea. The content of hypersthene increased significantly on the outer shelf of the Chukchi Sea. The garnet was derived from volcanic rocks of the Okhotsk-Chukotka volcanic province and transported from the Gulf of Anadyr by the Pacific inflow. Coastal erosion materials dominated in the inner shelf of the Chukchi Sea. A significant amount of river input occurred in the western, middle, and eastern parts of the East Siberian Sea. The inputs from the Indigirka River and Kolyma River tend to be distributed eastward. The garnet geochemistry shows that there was a mixed sedimentary zone located south of Wrangel Island. The sediments in the outer shelf of the East Siberian Sea show a stable mixed sedimentary environment. [ABSTRACT FROM AUTHOR]

Abstract: There are several micro-blocks dispersed in the South China Sea (SCS), e.g., Xisha-Zhongsha block, Nansha block and Reed-Northeastern Palawan block, etc., but detailed petrological constraints on their basement nature were previously lacking. The magmatic ages for granitic rock samples from two dredge stations in the Nansha micro-block vary from 159 to 127Ma, which are comparable to magmatic activities occurred in the northern margin (Pearl river mouth), HongKong and East China. Petrographic characteristics, major-, trace element and Sr–Nd isotopic data of nine samples from two dredged station performed in the Nansha micro-block, the SCS, are reported. Petrographically, these granitic rocks can be divided into two groups which underwent a complex history of magmatic process, i.e., tonalitic rock (Group I) and monzogranitic rock (Group II). The Rittmann index (σ) for these rocks (1.9–3.1) suggest that they belong to calc-alkaline rocks. Group I rocks which is of typical I-type, have higher contents of TiO2, Al2O3, FeO, MgO, CaO, Na2O and P2O5, but lower values of SiO2 and K2O, when compared with those of Group II with I-type characteristics. Group I rocks are produced by partial melting of older Precambrian basement with the variable influence of mantle-derived magma which results from the interaction of released fluids from the subducted slab and the overlying mantle wedge in a general convergent margin setting, and Group II rocks result from partial melting of lower crustal basic rocks (amphibolite) and/or further partial melting of the Group I rocks associated with the variable influence from the underplating mantle-derived magma resulting from lithospheric extensional regime. Both Groups I and II have undergone assimilation and fractional crystallization (AFC) processes during its petrogenesis. This study therefore demonstrates that there exists a continental basement within micro-blocks in the South China Sea, and further supports the idea that a Middle Jurassic to Mid-Cretaceous subduction zone existed across the temporary Taiwan, Palawan to Southern Vietnam, which was associated with westward to northestward convergence of the Pacific Plate during Late Mesozoic. We suggest that this subduction zone may have been connected with the paleo-Pacific plate subduction zone offshore eastern China during Mesozoic era. This study provides petrologic data for the pre-Cenozoic tectonic evolution of the South China Sea. [Copyright &y& Elsevier]