Re-assessment of the effect of fractional crystallization on Mo isotopes: Constraints from I-type granitoids and their enclosed mafic magmatic enclaves
Re-assessment of the effect of fractional crystallization on Mo isotopes: Constraints from I-type granitoids and their enclosed mafic magmatic enclaves
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重新评估分步结晶对Mo同位素的影响：来自I型花岗岩及其封闭的镁铁质岩浆包体的约束
DOI：
10.1016/j.chemgeo.2022.120814
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发表时间：
2022-03
期刊：
影响因子：
3.9
通讯作者：
Qiqi Xue
中科院分区：
文献类型：
--
作者：
Shuo Chen;Yaoling Niu;Hongmei Gong;Xiaohong Wang;Qiqi Xue
近年来，高温地质作用中钼同位素的研究取得了很大进展。但在岩浆分异过程中是否发生了Mo同位素分馏仍存在争议。在这里，我们重新评估岩浆分异对钼同位素分馏的影响，使用已发表的数据，结合我们的新的分析，在良好的特征I型花岗岩类和封闭的镁铁质岩浆包体（MMEs）在北祁连造山带的两个岩体中的钼同位素。在每个岩体中的MMEs，代表早期累积角闪石和黑云母的模态比例较大，显示出类似的钼元素和同位素组成，其主机花岗岩。两岩体中Mo同位素与Dy/Dy ~*、Fe_2 O_3和K/Rb比值均不存在协变，进一步表明角闪石、黑云母和富Fe ~（3+）矿物的分离结晶作用并不使两岩体中Mo同位素发生分离。在重新评估已发表的和我们新获得的钼同位素数据的基础上，我们发现，没有明确的证据表明，在岩浆岩分离结晶过程中的钼同位素分馏。样品的Mo同位素与Sr同位素和Rb/La比值呈正相关，与Nd同位素和Ce/Pb比值呈负相关，表明岩浆源区成分的变化控制了花岗岩类的Mo同位素组成变化。
In recent years, considerable progress has been made on the study of Mo isotopes in high-temperature geological processes. However, it is still controversial whether Mo isotope fractionation occurs during magmatic differentiation. Here we reassess the effect of magma differentiation on Mo isotope fractionation using published data in conjunction with our new analysis of Mo isotopes in well-characterized I-type granitoids and their enclosed mafic magmatic enclaves (MMEs) from two plutons in the North Qilian Orogen. The MMEs in each pluton, representing earlier cumulates with greater modal proportions of amphibole and biotite, show similar Mo elemental and isotopic compositions to their host granitoids. The absence of covariation of Mo isotopes with Dy/Dy*, Fe2O3and K/Rb in both plutons further indicates that fractional crystallization of amphibole, biotite and Fe3+-rich minerals does not fractionate Mo isotopes in these granitoids. On the basis of re-assessment of published and our newly obtained Mo isotope data, we find that there is no clear evidence for Mo isotope fractionation during fractional crystallization in igneous rock. Instead, Mo isotopes of our samples correlate positively with Sr isotopes and Rb/La ratios, and negatively with Nd isotopes and Ce/Pb ratios, indicating clearly that magma source compositional variation controls the variation of Mo isotope compositions of these granitoids.
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影响因子：
5.5
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