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doi:10.2204/iodp.proc.301.203.2008 ResultsLead isotope data on sediment samples were 18.913–19.172 for 206Pb/204Pb, 15.632–15.675 for 207Pb/204Pb, and 38.743–39.092 for 208Pb/204Pb (Table T1). Three samples from Sections 301-U1301C-4H-5, 11H-1, and 301-U1301D-5H-1 are described as slightly more radiogenic (206Pb/204Pb > 19.1) than other samples (206Pb/204Pb < 19.1) (Fig. F2). The Pb isotopic variation with depth profile of sediment cores is shown in Figure F3. With the exception of the three radiogenic samples (206Pb/204Pb > 19.1), the sediment samples display a slight decline in 206Pb/204Pb with increasing depth, whereas 207Pb/204Pb and 208Pb/204Pb are almost unchanged. The field defined by these sediment samples departs from the Juan de Fuca and Gorda Ridge basalt field (Fig. F2). The sediment data plot close to the field of surface sediments from the northern Juan de Fuca Ridge (Cousens et al., 2002) but demonstrate a wider range of variation. They are distinct from altered turbidites from the northern Juan de Fuca Ridge, although the trends defined by sediment samples are subparallel to the turbidites field. An interesting point is that the trends defined by these sediment samples extend at the lower 206Pb/204Pb end toward the Pacific seawater field represented by Mn crust (von Blanckenburg et al., 1996). Conversely, massive sulfides from the northern Juan de Fuca Ridge (Cousens et al., 2002) plot between the basalts field and sediments with steeper trend; Pb isotopic composition of the most radiogenic massive sulfides overlap our sediment samples with the lowest 206Pb/204Pb. |