The Hf–Nd isotopic composition of marine sediments
The Hf–Nd isotopic composition of marine sediments
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DOI：
10.1016/j.gca.2011.07.046
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发表时间：
2011-10
影响因子：
5
通讯作者：
J. Vervoort;T. Plank;J. Prytulak
中科院分区：
文献类型：
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作者：
J. Vervoort;T. Plank;J. Prytulak
本文介绍了新的主要和微量元素数据和Lu-Hf和Sm-Nd同位素组成的海洋沉积物样品的代表性套件从14个钻井现场外的世界主要俯冲带。这些套房和样品的选择，以代表全球范围内的岩性，Lu/Hf比值，并在全球范围内的俯冲沉积物的沉积物通量。这里报告的数据代表了最全面的数据集俯冲沉积物和定义的Hf-Nd同位素变化，发生在海洋沉积物和限制的过程，造成他们。利用新的海洋沉积物资料，结合已发表的资料，我们推导出一个新的陆地台阵，其公式为：εHf=1.55×εNd+1.21。该阵列是使用>3400个现今Hf和Nd同位素值计算的。与原始表达式（εHf=1.36×εNd+2.89; Vervoort等人，1999年）反映了使用的现代价值观和非放射性成因的Hf古老的大陆样品中包括的阵列。为了研究海洋沉积物中Hf-Nd同位素的变化，我们根据岩性和主要和微量元素的地球化学组成，将我们的样品分为5组：浊积岩，陆源粘土，火山岩，热液和水成沉积物。沿陆地阵列的成分沿着主要是由陆源物质来自大陆，并通过浊积岩，火山碎屑沉积物和火山岩浆弧输入到海洋盆地。地面阵列下方的成分来自富锆石浊积岩中的非放射成因铪。陆地阵列上方的异常成分在很大程度上反映了Hf和Nd在大陆风化和向海洋输送过程中的分离行为。陆源和水成粘土都具有强烈的放射成因Hf，一方面反映了陆源沉积和风化作用，另一方面反映了海相继承作用。这可能发生在补充过程中，涉及优先保留的非放射性Hf的形式在大陆上的锆石和释放的放射性Hf的分解容易风化，高Lu-Hf相，如磷灰石。
This paper presents new major and trace-element data and Lu–Hf and Sm–Nd isotopic compositions for representative suites of marine sediment samples from 14 drill sites outboard of the world’s major subduction zones. These suites and samples were chosen to represent the global range in lithology, Lu/Hf ratios, and sediment flux in subducting sediments worldwide. The data reported here represent the most comprehensive data set on subducting sediments and define the Hf–Nd isotopic variations that occur in oceanic sediments and constrain the processes that caused them. Using new marine sediment data presented here, in conjunction with published data, we derive a new Terrestrial Array given by the equation, εHf=1.55×εNd+1.21. This array was calculated using >3400 present-day Hf and Nd isotope values. The steeper slope and smaller y-intercept of this array, compared to the original expression (εHf=1.36×εNd+2.89; Vervoort et al., 1999) reflects the use of present day values and the unradiogenic Hf of old continental samples included in the array. In order to examine the Hf–Nd isotopic variations in marine sediments, we have classified our samples into 5 groups based on lithology and major and trace-element geochemical compositions: turbidites, terrigenous clays, and volcaniclastic, hydrothermal and hydrogenetic sediments. Compositions along the Terrestrial Array are largely controlled by terrigenous material derived from the continents and delivered to the ocean basins via turbidites, volcaniclastic sediments, and volcanic inputs from magmatic arcs. Compositions below the Terrestrial Array derive from unradiogenic Hf in zircon-rich turbidites. The anomalous compositions above the Terrestrial Array largely reflect the decoupled behavior of Hf and Nd during continental weathering and delivery to the ocean. Both terrigenous and hydrogenetic clays possess anomalously radiogenic Hf, reflecting terrestrial sedimentary and weathering processes on the one hand and marine inheritance on the other. This probably occurs during complementary processes involving preferential retention of unradiogenic Hf on the continents in the form of zircon and release of radiogenic Hf from the breakdown of easily weathered, high Lu–Hf phases such as apatite.