Coupling of anatectic reactions and dissolution of accessory phases and the Sr and Nd isotope systematics of anatectic melts from a metasedimentary source
Coupling of anatectic reactions and dissolution of accessory phases and the Sr and Nd isotope systematics of anatectic melts from a metasedimentary source
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DOI：
10.1016/j.gca.2005.02.035
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发表时间：
2005-07
影响因子：
5
通讯作者：
L. Zeng;P. Asimow;J. Saleeby
中科院分区：
文献类型：
--
作者：
L. Zeng;P. Asimow;J. Saleeby
在野外观测和实验岩石学的进展，深熔产物促使我们调查的地球化学后果的副矿物溶解和非模态部分熔融过程。将磷灰石和独居石溶解纳入白云母脱水熔融模型，使我们能够研究的Rb-Sr和Sm-Nd同位素系统的耦合在深熔熔体从白云母轴承变质沉积岩源。模拟结果表明：（1）熔体的Sm/Nd比值和Nd同位素组成取决于熔体中磷灰石和独居石的溶解量;（2）进入熔体的云母（白云母和黑云母）和长石（斜长石和钾长石）的相对比例是决定熔体Rb/Sr和87 Sr/86 Sr比值的关键参数。此外，这两个因素实际上并不是独立的。一般而言，泥质源的非模态部分熔融导致熔体在εNd-87 Sr/86 Sr比值空间中遵循两条路径之一。温度较高、无流体的路径（路径1）代表白云母/黑云母脱水和磷灰石而不是独居石溶解起重要作用的部分熔融反应;熔体将具有升高的Rb/Sr、87 Sr/86 Sr、Sm/Nd和ε Nd值。相比之下，较低的温度，流体流动路径（路径2）代表那些部分熔融反应，其中白云母/黑云母脱水起着微不足道的作用，磷灰石而不是独居石留在残留物中;熔体将具有较低的Rb/Sr，87 Sr/86 Sr，Sm/Nd和ε Nd值比它的源。控制副相溶解（因此Sm-Nd系统）和熔融反应（因此Rb-Sr系统）的主要变量是温度和水含量。在Sr-Nd同位素系统的复杂性在变质沉积物衍生的熔体，在这项研究中建议，将有助于我们更好地了解岩石成因的花岗岩岩体，具有显着的地壳源成分。
Advances in field observations and experimental petrology on anatectic products have motivated us to investigate the geochemical consequences of accessory mineral dissolution and nonmodal partial melting processes. Incorporation of apatite and monazite dissolution into a muscovite dehydration melting model allows us to examine the coupling of the Rb-Sr and Sm-Nd isotope systems in anatectic melts from a muscovite-bearing metasedimentary source. Modeling results show that (1) the Sm/Nd ratios and Nd isotopic compositions of the melts depend on the amount of apatite and monazite dissolved into the melt, and (2) the relative proportion of micas (muscovite and biotite) and feldspars (plagioclase and K-feldspar) that enter the melt is a key parameter determining the Rb/Sr and87Sr/86Sr ratios of the melt. Furthermore, these two factors are not, in practice, independent. In general, nonmodal partial melting of a pelitic source results in melts following one of two paths in εNd-87Sr/86Sr ratio space. A higher temperature, fluid-absent path (Path 1) represents those partial melting reactions in which muscovite/biotite dehydration and apatite but not monazite dissolution play a significant role; the melt will have elevated Rb/Sr,87Sr/86Sr, Sm/Nd, and εNdvalues. In contrast, a lower temperature, fluid-fluxed path (Path 2) represents those partial melting reactions in which muscovite/biotite dehydration plays an insignificant role and apatite but not monazite stays in the residue; the melt will have lower Rb/Sr,87Sr/86Sr, Sm/Nd, and εNdvalues than its source. The master variables controlling both accessory phase dissolution (and hence the Sm-Nd system), and melting reaction (and hence the Rb-Sr systematics) are temperature and water content. The complexity in Sr-Nd isotope systematics in metasediment-derived melts, as suggested in this study, will help us to better understand the petrogenesis for those granitic plutons that have a significant crustal source component.