熔体渗透过程中稳定的铬同位素分馏：对地幔中铬同位素非均质性的影响

IF 8.5 1区地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY

Geoscience frontiers Pub Date : 2025-04-17 DOI:10.1016/j.gsf.2025.102049

Haibo Ma , Li-Juan Xu , Yu-Wen Su , Chunyang Liu , Sheng-Ao Liu , Jia Liu , Zezhou Wang , Guochun Zhao

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引用次数: 0

摘要

为了研究地幔熔体渗透过程中稳定的铬（Cr）同位素变化，我们分析了意大利阿尔卑斯巴尔穆西亚和巴尔迪塞罗橄榄岩地块新鲜超镁质岩石的Cr同位素组成。这些地块代表了次大陆岩石圈地幔的碎片。所收集的样品包括黑橄榄岩、黑橄榄岩、泥质岩和辉石岩。锆石的δ53Cr值介于- 0.13‰±0.03‰至- 0.03‰±0.03‰之间。这些值与Al2O3含量呈负相关，表明部分熔融导致熔体与残余橄榄岩之间的Cr同位素分馏。哈尔茨伯尔岩和邓恩岩受硅酸盐熔体渗流影响，δ53Cr值明显不同。值得注意的是，与辉石岩脉没有空间关联的泥质岩δ53Cr值相对于辉石岩略高（- 0.05‰±0.03‰~ 0.10‰±0.03‰）。这种差异可能是熔融渗透过程中辉石溶解和橄榄石沉淀的结果。而与辉石岩脉直接接触的一种白云石样品δ53Cr值较低（- 0.26‰±0.03‰），可能与硅酸盐熔体渗流的动力学作用有关。辉石岩是玄武岩熔体与周围的橄榄岩通过交代反应或在脉中结晶作用形成的。大部分δ53Cr值（- 0.26‰±0.03‰~ - 0.13‰±0.03‰）与MgO含量呈正相关，表明它们受岩浆分异的影响。然而，同一斜辉石岩脉的两个亚样品δ53Cr值异常低（- 0.30‰±0.03‰和- 0.43‰±0.03‰），这归因于熔体渗透过程中的动力学同位素分馏作用。我们的研究结果表明，地幔中的熔融渗透过程有助于地幔中观测到的Cr同位素非均质性。

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$Stable chromium isotope fractionation during melt percolation: Implications for chromium isotopic heterogeneity in the mantle$

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Stable chromium isotope fractionation during melt percolation: Implications for chromium isotopic heterogeneity in the mantle

To investigate the stable chromium (Cr) isotope variations during melt percolation in the mantle, we analyzed the Cr isotopic compositions of fresh ultramafic rocks from the Balmuccia and Baldissero peridotite massifs located in the Italian Alps. These massifs represent fragments of the subcontinental lithospheric mantle. The samples collected included lherzolites, harzburgites, dunites, and pyroxenites. Lherzolites, formed through 5%–15% fractional melting of a primitive mantle source, exhibited δ⁵³Cr values ranging from −0.13‰ ± 0.03‰ to −0.03‰ ± 0.03‰. These values correlated negatively with Al₂O₃ content, suggesting that partial melting induces Cr isotopic fractionation between the melts and residual peridotites. Harzburgites and dunites, influenced by the silicate melt percolation, displayed distinct δ⁵³Cr values. Notably, dunites not spatially associated with the pyroxenite veins exhibited slightly elevated δ⁵³Cr values (−0.05‰ ± 0.03‰ to 0.10‰ ± 0.03‰) relative to lherzolites. This difference likely resulted from pyroxene dissolution and olivine precipitation during melt percolation processes. However, one dunite sample in direct contact with pyroxenite veins showed lower δ⁵³Cr values (−0.26‰ ± 0.03‰), possibly owing to the kinetic effects during silicate melt percolation. Pyroxenites are formed through the interaction of basaltic melts with the surrounding peridotite via a metasomatic reaction or crystallization in a vein. Most of their δ⁵³Cr values (−0.26‰ ± 0.03‰ to −0.13‰ ± 0.03‰) are positively correlated with MgO contents, suggesting that they were influenced by magmatic differentiation. However, two subsamples from a single clinopyroxenite vein exhibit anomalously low δ⁵³Cr values (−0.30‰ ± 0.03‰ and −0.43‰ ± 0.03‰), which are attributed to kinetic isotopic fractionation during melt-percolation processes. Our findings suggest that melt percolation processes in the mantle contribute to the Cr isotopic heterogeneity observed within the Earth’s mantle.

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来源期刊

Geoscience frontiers Earth and Planetary Sciences-General Earth and Planetary Sciences

CiteScore

17.80

自引率

3.40%

发文量

147

审稿时长

35 days

期刊介绍： Geoscience Frontiers (GSF) is the Journal of China University of Geosciences (Beijing) and Peking University. It publishes peer-reviewed research articles and reviews in interdisciplinary fields of Earth and Planetary Sciences. GSF covers various research areas including petrology and geochemistry, lithospheric architecture and mantle dynamics, global tectonics, economic geology and fuel exploration, geophysics, stratigraphy and paleontology, environmental and engineering geology, astrogeology, and the nexus of resources-energy-emissions-climate under Sustainable Development Goals. The journal aims to bridge innovative, provocative, and challenging concepts and models in these fields, providing insights on correlations and evolution.