| 东太平洋海隆热液活动区沉积岩心的地球化学研究 |
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| 关键词:hydrothermal activity sediment cores geochemistry Carbon-14 ages East Pacific Rise |
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| Geochemical Studies of Sediment Cores from the Hydrothermal Field on the East Pacific Rise |
| The East Pacific Rise is one of the tectonic environments characterized by very abundant modern hydrothermal activities and hydrothermal sediments. Two sediment cores from the hydrothermal fields near the EPR 13°N were chosen for systematic elemental geochemical analysis. The analytical techniques used included Inductively Coupled Plasmas-Atomic Emission Spectroscopy (ICP-AES) and Inductively Coupled Plasmas-Mass Spectrometry (ICP-MS). In addition, the Carbon-14 ages of some foraminifer samples in the selected layers were measured by AMS. 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 weakly positively correlated or negatively correlated with Al,Na,Ca,Mg and Ti.All this indicates that most trace elements and REE are probably scavenged by Fe-Mn oxyhydroxide materials from hydrothermal fluids and seawater. In the upper Core B13-62,the concentrations and distribution of the elements are similar to those in Core B13-26. In the lower parts,the contents of Fe and Mn decrease,while the content of Al increases distinctly, with little or no hydrothermal signature. As the distances between the two cores and the ridge axis or the vents are different,the hydrothermal signatures preserved in the two cores behave differently. The common characteristic of the two cores is that Ca and Sr in both cores are negatively or slightly positively correlated with other elements. Carbon-14 ages of sediments from different layers between 35～250cm below the seafloor in Core B13-26 shows a limited range from 10500 to 12000 years B P,with the difference of only several hundred years,even lower than the errors.Combined with the distribution pattens of typical hydrothermal components along the core,it is held that the sediments in Core B13-26 have recorded an intense hydrothermal event with a high sedimentation rate. This event should have started from 12000 yr B P and weakened a little 10000 yr B P. Carbon-14 age of the foraminifer in the sediments at 45～50cm below the seafloor from Core B13-62 is 32900±530 years B P. Owing to the limitation of this dating method,the age of sediments at 135～140cm below the seafloor was not acquired. It should be older than 40000 years B P. Obviously, Core B13-26 was not affected by the hydrothermal activities at the early period,and with a low sedimentation rate. Only recently,in the upper 0～35cm,the sediments were affected by hydrothermal activities,resulting in the enrichment of Fe,Mn,Zn,Cr,Co,Ni,V,etc. |
| XUE Fayu,ZHAI Shikui.2005.Geochemical Studies of Sediment Cores from the Hydrothermal Field on the East Pacific Rise[J].Acta Geoscientica Sinica,26(z1):200-201. |
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