Quantification of the lanthanide tetrad effect and its correlation with K/Rb, Eu/Eu*, Sr/Eu, Y/Ho, and Zr/Hf of evolving peraluminous granite suites
Quantification of the lanthanide tetrad effect and its correlation with K/Rb, Eu/Eu*, Sr/Eu, Y/Ho, and Zr/Hf of evolving peraluminous granite suites
复制标题
DOI：
10.1016/s0016-7037(99)00027-7
复制
发表时间：
1999-02
影响因子：
5
通讯作者：
W. Irber
中科院分区：
文献类型：
--
作者：
W. Irber
在德国中东部（中部厄尔士山脉、西部厄尔士山脉、菲希特山脉和北方上普法尔茨）更高度演化的华力西期过铝花岗岩的稀土元素模式中，经常观察到镧系元素四分体效应。四分体效应的程度（TE 1，3）的估计和绘制与K/Rb，Sr/Eu，Eu/Eu的Hf，Y/Ho，和Zr/Hf。图解表明，四分体效应的发展与花岗岩的演化平行，并且显著的四分体效应严格限于高度分异的样品。矿物分馏作为四分体效应的原因是不支持由计算的瑞利分馏，这也不能解释的分馏趋势的Sr/Eu和Eu/Eu Eu的。在高度演化的岩石中Eu浓度的强烈下降表明，Eu分馏之间的残留熔体和共存的含水高温流体。矿物分馏作为四分体效应的原因是更不可能的稀土元素模式的副矿物显示类似的四分体效应作为各自的主机岩石。副矿物继承了稀土元素的签名熔体，并没有通过矿物分馏的大块岩石四分体效应。这些结果表明，在高度演化的花岗岩熔体中，元素分馏行为发生了显著变化：通常控制矿物和熔体之间元素分布的离子半径和电荷不再是唯一的控制因素。四分体效应和Y/Ho和Zr/Hf的高度分馏微量元素比表明微量元素的行为与化学络合作用具有显着影响的含水系统中的行为相似。这种独特的微量元素行为和岩浆热液蚀变的共同特征表明，在花岗岩结晶的最后阶段，一个含水的流体系统的重要性越来越大。TE_（1，3）与岩石整体氟含量的正相关关系表明稀土元素氟络合作用在四分体效应产生中的重要性。由于四分体效应（M型）的稀土元素模式的演变意味着相应的镜像稀土元素模式（W型）的去除，四分体效应识别花岗岩结晶过程中的开放系统条件。
Lanthanide tetrad effects are often observed in REE patterns of more highly evolved Variscan peraluminous granites of mid-eastern Germany (Central Erzgebirge, Western Erzgebirge, Fichtelgebirge, and Northern Oberpfalz). The degree of the tetrad effect (TE1,3) is estimated and plotted vs. K/Rb, Sr/Eu, Eu/Eu∗, Y/Ho, and Zr/Hf. The diagrams reveal that the tetrad effect develops parallel to granite evolution, and significant tetrad effects are strictly confined to highly differentiated samples. Mineral fractionation as a cause for the tetrad effect is not supported by a calculated Rayleigh fractionation, which also could not explain the fractionation trends of Sr/Eu and Eu/Eu∗. The strong decrease of Eu concentrations in highly evolved rocks suggests that Eu fractionates between the residual melt and a coexisting aqueous high-temperature fluid. Mineral fractionation as a reason for the tetrad effect is even more unlikely as REE patterns of accessory minerals display similar tetrad effects as the respective host rocks. The accessory minerals inherit the REE signature of the melt and do not contribute to the bulk-rock tetrad effect via mineral fractionation. These results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts: ionic radius and charge, which commonly control the element distribution between mineral and melt, are no longer the exclusive control. The tetrad effect and the highly fractionated trace element ratios of Y/Ho and Zr/Hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence. This distinct trace element behavior and the common features of magmatic-hydrothermal alteration suggest the increasing importance of an aqueous-like fluid system during the final stages of granite crystallization. The positive correlation of TE1,3with bulk-rock fluorine contents hints at the importance of REE fluorine complexation in generating the tetrad effect. As the evolution of a REE pattern with tetrad effect (M-type) implies the removal of a respective mirroring REE pattern (W-type), the tetrad effect identifies open system conditions during granite crystallization.