From sediments to their source rocks: Hf and Nd isotopes in recent river sediments
From sediments to their source rocks: Hf and Nd isotopes in recent river sediments
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DOI：
10.1130/g31785.1
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发表时间：
2011-04-01
期刊：
影响因子：
5.8
通讯作者：
Cawood, Peter A.
中科院分区：
文献类型：
--
作者：
Dhuime, Bruno;Hawkesworth, C. J.;Cawood, Peter A.
从沉积记录中揭示大陆演化需要了解将沉积物与其源岩联系起来的时间综合侵蚀规律，以及侵蚀规律在不同侵蚀系统中的变化程度。来自弗兰克兰河（澳大利亚西南部）的碎屑锆石定义了一条大陆生长曲线，该曲线与澳大利亚大陆页岩中的Nd曲线惊人地相似。这表明，碎屑锆石数据可以作为一个很好的替代沉积记录通过时间。其优点是，锆石的年龄分布允许从不同的源区的贡献，以确定任何沉积物样品。使用集成的Hf和U-Pb同位素在碎屑锆石，和Nd同位素比值的散装最近沉积物沿着弗兰克兰河，不同的源地形的相对贡献已被确定和表示通过侵蚀参数K，它涉及到的比例，从不同的源岩的沉积物中的物质的比例，这些源岩的存在于整个流域的沉积物分析。结果表明，K = 4-6的值代表了采样大源区的成熟河流系统，这些值应用于重新评估通常受到K假设限制的大陆地壳演化模型。对于冈瓦纳超大陆，K值为4-6表明现今大陆地壳体积的至少50%是在太古代末期形成的。
Unraveling continental evolution from the sedimentary record requires an understanding of time-integrated erosion laws that link sediments to their source rocks, and the extent to which erosion laws vary in different erosion systems. Detrital zircons from the Frankland River (southwestern Australia) define a continental growth curve that is strikingly similar to the Nd in shales curve for the Australian continent. This suggests that the detrital zircon data can be used as a good proxy for the sedimentary record through time. The advantage is that the age distribution of the zircons allows the contributions from different source regions to be determined for any sediment sample. Using integrated Hf and U-Pb isotopes in detrital zircons, and Nd isotope ratios of bulk recent sediments along the Frankland River, the relative contributions of different source terrains have been determined and expressed through an erosion parameter K, which relates the proportions of the material from different source rocks in the sediments to the proportions of those source rocks present in the overall catchment of the sediments analyzed. The results suggest that values of K = 4-6 are representative of mature river systems that sample large source areas, and that these should be used to reevaluate models of the evolution of the continental crust that were generally limited by the assumption of K. For the Gondwana supercontinent, K values of 4-6 indicate that at least 50% of the present-day volume of the continental crust was generated by the end of the Archean.