近日，同济大学张灵敏团队报道了西南印度洋脊磷灰石揭示的地幔氯同位素特征及熔融岩相互作用。2025年11月19日出版的《地质学》杂志发表了这项成果。

地幔中氯同位素的不均一性程度仍是活跃的争议焦点。为推进这一讨论，研究组首次对综合大洋钻探计划U1473A钻孔（西南印度洋中脊）辉长岩中的磷灰石进行了原位氯同位素测定。这些磷灰石记录了-0.51‰ ± 0.04‰的原始地幔δ³⁷Cl值，与全球洋中脊玄武岩平均值一致。δ³⁷Cl与氯含量在岩性边界呈现的系统性负协变关系无法仅用结晶分异作用解释。与大洋钻探计划735B钻孔（大西洋银行）蚀变辉长岩相比，U1473A磷灰石显示出更低的δ³⁷Cl值。

这些磷灰石完好保存的自形晶结构与稳定的羟基浓度，结合角闪石地球化学数据，共同排除了低温海水蚀变的影响。相反，这些特征反映了熔岩相互作用、卤水同化或地幔不均一性等高温过程。该研究结果表明，地幔来源磷灰石中的δ³⁷Cl变化既记录了地壳再循环信号，也反映了地幔内在的不均一性，证实其可作为深部地球挥发分循环的可靠示踪剂。

附：英文原文

Title: Mantle chlorine isotope signature and melt-rock interaction revealed by apatite at the Southwest Indian Ridge

Author: Naixiao Xu, Hao Cheng, Geoffrey D. Bromiley, Henry J.B. Dick, Lingmin Zhang

Issue&Volume: 2025-11-19

Abstract: The extent of chlorine isotope heterogeneity within Earth’s mantle remains a subject of active debate. To contribute to this discussion, we present the first in situ chlorine isotope measurements of apatite from Integrated Ocean Drilling Program Hole U1473A (Southwest Indian Ridge) gabbros. The apatites record a pristine mantle δ37Cl value of 0.51‰ ± 0.04‰, consistent with global mid-ocean ridge basalt averages. Systematic negative covariations between δ37Cl and Cl content across lithological boundaries cannot be explained by fractional crystallization alone. Compared to altered gabbros from Ocean Drilling Program Hole 735B (Atlantis Bank), apatites from U1473A show lower δ37Cl values. The preservation of euhedral textures and constant OH concentrations in these apatites, combined with amphibole geochemistry, rules out lower-temperature seawater alteration. Instead, these trends reflect high-temperature processes, including meltrock interaction, brine assimilation, or mantle heterogeneity. Our findings demonstrate that δ37Cl variability in mantle-derived apatites records both crustal recycling and intrinsic mantle heterogeneity, confirming their utility as reliable tracers of deep Earth volatile cycling.

DOI: 10.1130/G53563.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G53563.1/697024/Mantle-chlorine-isotope-signature-and-melt-rockredirectedFrom=fulltext