|Budget Amount *help
¥2,400,000 (Direct Cost : ¥2,400,000)
Fiscal Year 1997 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1996 : ¥1,700,000 (Direct Cost : ¥1,700,000)
This project included : (1) Provenance signatures and evolution of Cretaceous clastic sediments and (2) Chemistry of Miocene sediments in the San'in region.
(1) Cretaceous : Sample suites were collected across the Shimanto terrane in Kii Peninsula, to determine stratigraphic changes in provenance signatures. Sediment chemistry shows progressive changes related to initial primary source contrasts, episodic weathering, heavy mineral concentration and possible superimposed cannibalistic recycling. The chemistry confirms that the Shimanto source was an evolved continental arc margin.
Sample suits were also collected from Cretaceous sequences in the Uisong and Milyang blocks of the Kyongsang Supergroup in Korea, and from the Kanmon Group in Yamaguchi, to test spatial variation at the Asian continental margin, and to compare with coeval Shimanto sediments in the Outer Zone. Results to date from the Uisong suite are consistent with derivation from Archean granitoids and high-grade metamorphic t
erranes, in contrast to the continental ar source of the Shimanto.
(2) Miocene : This concentrated on analysis of sediments from the Ushikiri and Matsue Formations, when volcanism in the source area changed from calcalkaline to alkaline. Ushikiri data reflect andesitic volcanic source, but overlying Matsue Formation compositions have highly evolved chemical signatures more typical of continental margins. This is a product of deep weathering of a primarily granitic source, exposed after stripping of overlying andesitic formations from which the Ushikiri Formation was derived. Although coeval alkaline volcanism occurs in the Matsue Formation, contribution to the sedimentary pile is minimal. The atypical nature of the Matsue sediments, and the role of weathering and sorting underscore difficulties in differentiation of tectonic setting in backarc environments. This emphasises the importance of aiming whole rock chemical studies of sediments towards estimating average bulk source composition, weathering history and sedimentary fractionation effects, rather than identifying depositional setting using rigid tectonic setting models. Less