澳大利亚国立大学 Yajie Gao 课题组研究了石榴子石与角闪石对于岩浆分异和板块熔融的意义。2023年11月30日出版的《地质学》杂志发表了这项成果。

研究发现，石榴子石特征可以用球粒陨石标准化稀土模式的形状系数来量化。研究人员将这种方法应用于全球数据集、新生代和第四纪的被称为“埃达克岩”的火山样品中。结果表明，许多(但不是全部)埃达克岩，经历了石榴子石的分离结晶作用，这种结晶作用从母岩熔融开始，归因于含石榴子石来源的部分熔体。

在许多例子中看到的极端石榴子石特征，需要混合来源，包括俯冲沉积物和火成岩洋壳；然而，广泛的地壳深部分异掩盖了这些来源的主要元素和微量元素特征，使人们对它们是否作为原始板熔体的身份产生了怀疑。

据介绍，埃达克岩中稀土元素(REE)丰度的石榴子石特征，被认为是这些有争议的岩石的关键成因指标，其起源可能包括俯冲洋壳的直接熔融(“板片熔体”)。

附：英文原文

Title: Garnet versus amphibole: Implications for magmatic differentiation and slab melting

Author: Yajie Gao, Hugh St. C. O’Neill, John A. Mavrogenes

Issue&Volume: 2023-11-30

Abstract: The garnet signature in the rare earth element (REE) abundances in adakites has been considered a key genetic indicator of these controversial rocks, whose proposed origins include direct melting of subducted oceanic crust (“slab melts”). We show that the garnet signature may be quantified using the shape coefficients of chondrite-normalized REE patterns. We applied this method to a global data set of Cenozoic and Quaternary volcanic samples described as “adakites.” The results indicate that many, but not all, suites of rocks labeled as adakites have undergone fractional crystallization of garnet, starting from parental melts attributable to partial melts of garnet-bearing sources. The extreme garnet signatures seen in many examples require hybrid sources, consisting of subducted sediment as well as igneous oceanic crust; however, extensive deep-crustal differentiation obscures the major and trace-element characteristics of these sources, casting doubt on their identification as primitive slab melts.

DOI: 10.1130/G51637.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G51637.1/629961/Garnet-versus-amphibole-Implications-for-magmatic