13. GEOCHEMISTRY OF SEDIMENTS AND AUTHIGENIC MINERALS IN AND AROUND THE DÉCOLLEMENT ZONE OF THE NORTHERN BARBADOS RIDGE ACCRETIONARY PRISM 1

T. Ito, 2 K. Yamaguchi,3 K. Komuro,3 Y. Ogawa 3

ABSTRACT

Chemical analyses for major and trace constituents of authigenic minerals and sediments collected in the northern Barbados Ridge during Ocean Drilling Program Leg 156 have been carried out. In addition to Mn enrichments previously reported, Cu enrichments were identified in this study.

Two kinds of Mn enrichments of rhodochrosite and amorphous Mn oxide occur at Site 948. Both of them have rare-earth element (REE) abundances similar to the North American Shale Composites and typical sediments recovered during Leg 156. Cu enrichments occur just above the décollement zone at Site 948, and also just above an inferred thrust based on the drastic change in interstitial-water chemistry at Site 949. The Cu-enriched parts are characterized by K, Ba, Cr, and light REE depletions.

1 Shipley, T.H., Ogawa, Y., Blum, P., and Bahr, J.M. (Eds.), 1997. Proc. ODP, Sci. Results,156: College Station, TX (Ocean Drilling Program).
2 Faculty of Education, Ibaraki University, Mito, Ibaraki, 310, Japan. tito@mito.ipc.ibaraki.ac.jp
3 Institute of Geoscience, University of Tsukuba, Tsukuba, Ibaraki, 305, Japan.