Tracing the deep geological water cycle requires knowledge of the hydrogen isotope systematics between and within hydrous materials. For quenched hydrous alkali-silicate melts, hydrogen NMR reveals a distinct heterogeneity in the distribution of stable hydrogen isotopes (D, H) within the silicate tetrahedral network, where deuterons concentrate strongly in network regions that are associated with alkali cations. Previous hydrogen NMR studies performed in the sodium tetrasilicate system (Na₂O x 4SiO₂, NS4) with a 1:1 D₂O/H₂O ratio showed on average 1300 ‰ deuterium enrichment in the alkali-associated network, but the effect on varying bulk D₂O/H₂O ratios on this intramolecular isotope effect remained unconstrained. Experiments in the hydrous sodium tetrasilicate system with 8 wt% bulk water and varying bulk D₂O/H₂O ratios were performed at 1400 °C and 1.5 GPa. It is found that both hydrogen isotopes preferably partition into the silicate network that is associated with alkali ions. The partitioning is always stronger for the deuterated than for the protonated hydrous species. The relative enrichment of deuterium over protium in the alkali-associated network, i.e., the intramolecular isotope effect, correlates positively with the D₂O/H₂O bulk ratio of the hydrous NS4 system. Modeled for natural deuterium abundance (D/H near 1.56 × 10⁻⁴), a 1.4-fold (c. 340 ‰) deuterium enrichment in the alkali-associated silicate network is predicted. The partitioning model further predicts a positive correlation between the bulk water content of the silicate melt and the intramolecular deuterium partitioning into the alkali-associated silicate network. Such heterogeneities may explain the magnitude and direction of hydrogen isotope fractionation in hydrous silicate melts coexisting with silicate-saturated fluids. As such, this intramolecular isotope effect appears to be an effective mechanism for deuterium separation, particularly in hydrous magmatic settings, such as subduction zones.

追踪深层地质水循环需要了解含水材料之间和内部的氢同位素系统学。对于淬火的含水碱金属硅酸盐熔体，氢核磁共振揭示了硅酸盐四面体网络内稳定氢同位素（D，H）分布的明显异质性，其中氘核强烈集中在与碱金属阳离子相关的网络区域。先前在四硅酸钠体系（Na ₂ O x 4SiO ₂ ，​​NS4）中进行的氢核磁共振研究（Na 2 O x 4SiO 2 ，​​NS4）显示，碱金属相关网络中的氘平均富集度为 1:1 D ₂ O/H ₂ O，但效果在不同体积 D ₂ O/H ₂这种分子内同位素效应的 O 比率仍然不受限制。在 1400 °C 和 1.5 GPa 的条件下，在含水四硅酸钠系统中进行了实验，该系统具有 8 wt% 的本体水和不同的本体 D ₂ O/H _{2 O 比率。}发现两种氢同位素都优选分配到与碱金属离子相关的硅酸盐网络中。氘化的分配总是比质子化的含水物种更强。碱相关网络中氘相对于氕的相对富集，即分子内同位素效应，与含水NS4系统的D ₂ O/H ₂ O体积比正相关。模拟自然氘丰度（D/H 接近 1.56 × 10 ^-4)，预计碱金属相关的硅酸盐网络中的氘富集是 1.4 倍 (c. 340 ‰)。分配模型进一步预测了硅酸盐熔体的本体含水量与分子内氘分配到碱金属相关的硅酸盐网络中的正相关性。这种非均质性可以解释与硅酸盐饱和流体共存的含水硅酸盐熔体中氢同位素分馏的幅度和方向。因此，这种分子内同位素效应似乎是氘分离的有效机制，特别是在含水岩浆环境中，例如俯冲带。