Abstract Crystal-melt separation is important for understanding the evolution of granitic magma and the connection between plutonic and volcanic rocks. Crystal accumulation and melt extraction are the two key factors in the separation process. However, the existing geochemical indicators for crystal-melt separation in many granitic plutons are largely concealed by the remaining interstitial melt. Here, we report Ba isotope compositions of well-characterized Huili granitic pluton and associated mineral separates from the Jiaobei Terrane in the North China Craton. The Ba isotopes are significantly fractionated between the two types of granites in the Huili pluton. The more differentiated albite granites (AG) have heavier isotope compositions (δ138/134BaAG = 0.50–0.95‰) than the K-feldspar granites (KG) (δ138/134BaKG = −0.14 to 0.16‰). The δ138/134Ba of the whole-rocks change in the same manner as multiple element contents (such as K, Ba, and Sr). Trace element modeling suggests that such variations can be explained by K-feldspar-controlled crystal-melt separation in a K-rich granitic magma. As the K-feldspar granites represent the residual crystal mush, the Ba isotope data of the coexisting Ba-bearing minerals can impose critical constraints on crystal-melt separation. The K-feldspar shows the highest Ba content (387–1465 μg/g) and the lowest δ138/134Ba (−0.23 to 0.01‰) among all the investigated minerals, suggesting that its crystallization should drive the interstitial Na- and Si-rich melt towards an isotopically heavy composition. The apparent fractionation values of coexisting biotite and muscovite ( Δ 138 / 134 B a B i o t i t e - M u s c o v i t e ) vary from −0.98 to 1.01‰, indicating that the coexisting minerals are not in Ba isotope equilibrium. Combined with microstructural features, the Ba isotope disequilibrium signatures of coexisting minerals most likely reflect crystal accumulation and repacking during crystal-melt separation, providing a novel geochemical indicator for identifying the granitic plutons that represent residual crystal mush in the mid- to upper-crust. This study indicates that Ba isotopes are useful for deciphering petrogenetic links between intrusive and extrusive rocks.

中文翻译：

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花岗岩岩浆储层中晶体-熔体分离的钡同位素证据

摘要 结晶-熔体分离对于理解花岗质岩浆的演化以及深成岩与火山岩的联系具有重要意义。晶体积累和熔体提取是分离过程中的两个关键因素。然而，许多花岗岩岩体中晶体熔体分离的现有地球化学指标在很大程度上被剩余的间隙熔体所掩盖。在这里，我们报告了从华北克拉通胶北地体中分离出来的特征良好的惠里花岗质岩体和伴生矿物的 Ba 同位素组成。Ba同位素在惠立岩体中两类花岗岩之间分异显着。分化程度更高的钠长石花岗岩 (AG) 的同位素组成 (δ138/134BaAG = 0.50–0.95‰) 比钾长石花岗岩 (KG) (δ138/134BaKG = -0.14 到 0.16‰) 重。全岩δ138/134Ba的变化方式与多种元素含量（如K、Ba、Sr）相同。微量元素模型表明，这种变化可以通过富钾花岗岩岩浆中钾长石控制的晶体-熔体分离来解释。由于钾长石花岗岩代表残余结晶糊状物，共存含钡矿物的钡同位素数据可以对晶体-熔体分离施加关键约束。在所有研究的矿物中，钾长石显示出最高的 Ba 含量（387-1465 μg/g）和最低的 δ138/134Ba（-0.23 至 0.01‰），表明其结晶应驱动间隙富 Na 和 Si熔化成同位素重的成分。共存的黑云母和白云母的表观分馏值 (Δ 138 / 134 B a B iotite - M uscovite ) 从 -0.98 到 1 不等。01‰，说明共存矿物不处于Ba同位素平衡。结合微观结构特征，共存矿物的Ba同位素不平衡特征最有可能反映晶体-熔体分离过程中晶体的积累和重新堆积，为识别代表中上地壳残留结晶糊状物的花岗岩岩体提供了一种新的地球化学指标。这项研究表明，Ba 同位素可用于破译侵入岩和喷出岩之间的岩石成因联系。提供了一种新的地球化学指标，用于识别代表中上地壳残余结晶糊状物的花岗岩岩体。这项研究表明，Ba 同位素可用于破译侵入岩和喷出岩之间的岩石成因联系。提供了一种新的地球化学指标，用于识别代表中上地壳残余结晶糊状物的花岗岩岩体。这项研究表明，Ba 同位素可用于破译侵入岩和喷出岩之间的岩石成因联系。