Hydrogen incorporation and charge balance in natural zircon
Hydrogen incorporation and charge balance in natural zircon
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DOI：
10.1016/j.gca.2014.06.033
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发表时间：
2014-09-15
影响因子：
5
通讯作者：
Hellebrand, E.
中科院分区：
文献类型：
--
作者：
De Hoog, J. C. M.;Lissenberg, C. J.;Hellebrand, E.
测定了天然火成锆石中水和微量元素的含量，以制约氢的掺入机制。低辐射损伤锆石来自于Vema断裂带（北纬11度，大西洋中脊）的铁-钛氧化物辉长岩。它们含有高达1212 ppmw的H2O，1.9 wt.% Y2 O3和0.6重量% P2 O 5和一般强烈分区。REE + Y被P部分电荷平衡（Y，REE ~（3+）+P ~（5+）= Zr ~（4+）+Si ~（4+）），但存在较大的REE过剩。在原子的基础上，这种过量与锆石中存在的H的量非常接近。因此，我们得出结论，H是通过电荷平衡机制（H+ + REE 3 + = Zr 4+）结合的。这一解释与Vema锆石的FTIR数据相一致，该数据显示在约1000 nm处有一个强偏振的主吸收带。3100 cm（-1），类似于实验生长的掺Lu的水合锆石。这个3100 cm（-1）带的大小与H和REE含量成正比。除了在3200 cm（-1）处的一个小的重叠带外，没有其他可见的吸收带，这表明在这些锆石中似乎没有氢钙铝型交换机制。由于锆石中H、P和REE的电荷平衡吸收，这些元素在锆石中的分配取决于它们各自的浓度。例如，D-zrc/熔体（REE）随着熔体中H和P含量的增加而增加，而D-zrc/熔体（H）随着REE含量的增加而增加，但随着P含量的增加而减少。此外，H-P-REE扇形分带系统表明动力学效应可能起着重要作用。因此，使用锆石中的H来确定熔体的水含量是有问题的，并且REE分配研究需要考虑熔体的P和H2O含量。版权所有（C）2014由爱思唯尔有限公司发布。
The water and trace element contents of natural igneous zircons were determined to constrain the mechanism of hydrogen incorporation. The low radiation-damage zircons were derived from Fe-Ti oxide gabbros from the Vema Fracture Zone (11 degrees N, Mid-Atlantic Ridge). They contain up to 1212 ppmw H2O, 1.9 wt.% Y2O3 and 0.6 wt.% P2O5 and are generally strongly zoned. REE + Y are partially charge-balanced by P (Y, REE3+ + P5+ = Zr4+ + Si4+), but a large REE excess is present. On an atomic basis, this excess is closely approximated by the amount of H present in the zircons. We therefore conclude that H is incorporated by a charge-balance mechanism (H+ + REE3+ = Zr4+). This interpretation is consistent with FTIR data of the Vema zircons, which shows a strongly polarised main absorption band at ca. 3100 cm(-1), similar to experimentally grown Lu-doped hydrous zircon. The size of this 3100 cm(-1) band scales with H and REE contents. Apart from a small overlapping band at 3200 cm(-1), no other absorption bands are visible, indicating that a hydrogrossular-type exchange mechanism does not appear to be operating in these zircons. Because of charge-balanced uptake of H, P and REE in zircon, the partitioning of these elements into zircon is dependent on each of their concentrations. For instance, D-zrc/melt(REE) increases with increasing H and P contents of the melt, whereas D-zrc/melt(H) increases with increasing REE content but decreases with increasing P content. In addition, H-P-REE systematics of sector zoning indicate kinetic effects may play an important role. Hence, using H in zircon to determine the water content of melts is problematic, and REE partitioning studies need to take into account P and H2O contents of the melt. Crown copyright (C) 2014 Published by Elsevier Ltd.