| 摘要: |
| 80 Ma以来的海水Os同位素标准曲线具有K/T（白垩纪/第三纪）界线低值、E/O（始新世/渐新世）界线低值和中新世“挠曲”3个特征形态，这可以解释为陨击事件或超基性岩风化事件造成的陆、幔源物质供给关系的变化。将海水Os同位素标准曲线与多金属结壳Os同位素组成曲线进行对比，根据形态和取值的贴合程度可以为结壳进行年代厘定。由于取样精度的限制和生长间断的广泛存在，仅以此3个特征比对曲线存在不确定性。本研究综合对比中、西太平洋6块结壳的Os同位素组成曲线，总结出了4种记录在结壳中的海水Os同位素曲线的特征规律：K/T界线之前的“早期异常（波动）”；E/O界线之后曲线上升过程中的“小停顿”；E/O界线之后曲线上升过程末尾的“异常偏高点”；“中新世‘挠曲’错后”至10 Ma左右。这些新的特征形态可作为年代控制点，使得结壳年代框架的厘定可以更准确可靠。这4种特征形态可以初步解释为地质历史时期海洋中、幔源物质的供应关系变化或是看作随着数据的积累而对标准曲线的细化和校正。 |
| 关键词: 结壳 Os同位素 标准曲线 中、西太平洋 |
| DOI：10.11759/hykx20200203002 |
| 分类号:P67 |
| 基金项目:中国大洋矿产资源研究开发协会“十三五”资源环境项目（DY135-C1-1-06） |
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| Precise characteristics of Os isotopic composition of seawater since 80 Ma: recorded in polymetallic crusts from CW Pacific |
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WANG Yang, FANG Nian-qiao
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School of Ocean Science, China University of Geosciences, Beijing 100083, China
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| Abstract: |
| Since 80 Ma, the sea water Os isotopic standard curve has three characteristics:the low value at K/T (Cretaceous/Tertiary), the low value at E/O (Eocene/Oligocene) and the "kink" during Miocene, which can be explained as the change of material supply relationship between continent and mantle caused by the meteorite strike event or ultrabasic rock weathering event. By comparing the Os isotopic standard curve of sea water with that of polymetallic crusts, the age frame of it can be determined according to the value and shape fit. Because of the limitation of sampling accuracy and the wide existence of growth discontinuities, there is uncertainty in the comparison only based on these three features. In this study, the Os isotopic composition curves of six polymetallic crusts from the central western Pacific are compared, and four new characteristics of the sea water Os isotopic curves recorded in the crusts are summarized:(1) the "early anomaly (fluctuation)" before the K/T Boundary; (2) the "small pause" in the rising process after the E/O boundary; (3) the "abnormal higher point" at the end of the rising process after the E/O boundary and (4) the "kink malposition" at the end of the rising process after the E/O boundary to about 10 Ma. These new features can be used as age anchor points, making the determination of the age frame of polymetallic crusts more accurate, reliable and easy to operate. These four characteristics can be interpreted as the change of the supply relationship of continental and mantle derived materials in the geological history in the ocean or can be treated as the refinement and correction of the standard curve with the accumulation of data. |
| Key words: crust Os isotope standard curve central and western Pacific |
