| The East Pacific Rise is one of the tectonic environments with most abundant modern hydrothermal activities and hydrothermal sediments. The East Pacific Rise near 13°N has a high spreading rate about 12 centimeters per year, where there are frequent volcanic activities, abundant hydrothermal vents, thick sulphide deposits and multimetallic sediments. In recent years, EPR 13°N has become the focus of the studies on the hydrothermal activities and ore depositions on the fast spreading mid-ocean ridge.In this study, we chose two sediment cores drilled from the hydrothermal fields near the EPR 13° N, B13-26 and B13-62. The major and trace elements concentrations in the sediments were determined by Inductively Coupled Plasmas-Atomic Emission Spectroscopy(ICP-AES) and Inductively Coupled Plasmas-Mass Spectrometry(ICP-MS). At the same time, the Carbon-14 ages of some foraminifer samples in the selected layers were measured by AMS. Because the distances between two cores and the ridge axis or the vents are different, the hydrothermal signatures reserving in the two cores behave differently.Based on the study of sedimentology and mineralogy (Chen, 1997), systematic elemental geochemical and chronological analysis of the two cores have been conducted. The geochemical signatures tracing the hydrothermal activities were determined, and the variation rules of hydrothermal activities were discussed. The following conclusions were obtained:1. Core B13-26 mainly consists of metalliferous sediments near the ridge crest. The sediments are homogeneous brown carbonate-rich silty ooze. The pyrite minerals are abundant in the cores. Core B13-62 comprises mainly of metalliferous brown mud similar to Core B13-26 in the upper 30cm and grayish green or grayish yellow ooze in the lower 160 cm which are similar to normal pelagic carbonate and clay sediments. Between them there is a sharp colour change.2. The sediments are mainly amorphous in core B13-26. The crystallized minerals can be divided into two groups: the normal pelagic minerals and hydrothermal minerals. The upper Core B13-62 is similar to Core B13-26 in mineral assemblage, although a little higher clay minerals concentration. In the lower Core B13-62, the most abundant mineral is calcite.3. The sediments in Core B13-26 are enriched in typical hydrothermal components. Most trace elements and REE are well positively correlated with Fe and Mn, and are weak positively correlated or negatively correlated with Al, Na, Ca, Mg and Ti. This indicated that most trace elements and REE are probably scavenged by Fe-Mn oxyhydroxide materials from hydrothermal fluid and seawater.In the upper Core B13-62, the concentrations and distributions of the elements are similar to those in Core B13-26. In the lower parts, the contents of Fe and Mn decrease, however the content of Al increases distinctly, with little or no hydrothermal signature.The common characteristic of the two cores is that Ca and Sr in both cores are negatively or slightly positively correlated with other elements.4. Shale-normalised REE concentrations of the sediments in Core B13-26 show the pattern with HREE enrichment and negative Ce and Eu anomalies and positive Gd anomaly. More significantly, REE variations along the Core B13-26 are similar to Fe and Mn. This similarity indicates that REE contents are dominated by the adsorption of hydrothermal Fe- Mn oxyhydroxides.Shale-normalised REE distribution patterns in Core B13-62 is similar to that in core B13-26. The total REE content in core B13-62 is much lower than that in core B13-26, and REE variations along the core are not correlated with Fe and Mn.5. Carbon-14 ages of the sediments from the different layers between 35-250 cm below the seafloor in Core B13-26 shows a limited range from 10500 to 12000 years BP, with the difference of only several hundred years, even lower than the errors. Combined with the distribution patterns of typical hydrothermal components along the core, it suggests that the sediments in Core B13-26 record an intensive hy...
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