The stable Zr isotope composition of the martian mantle

IF 3.6 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Chemical Geology Pub Date : 2025-04-26 DOI:10.1016/j.chemgeo.2025.122811

Ninna K. Jensen , Zhengbin Deng , Martin Bizzarro

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Abstract

We report high-precision stable Zr isotope data for a wide selection of martian meteorites using the double-spike method. The investigated samples comprise shergottites, nakhlites, a single chassignite, and several clasts from the regolith breccia meteorite Northwest Africa (NWA) 7533. These samples are mostly of mafic compositions, and they exhibit limited, yet resolvable, stable Zr isotope compositions. Specifically, the range of δ⁹⁴Zr_IPGP-Zr compositions recorded by the SNC meteorites extends from 0.021 ± 0.003 ‰ (2SE) in Dhofar 019 to 0.093 ± 0.018 ‰ (2SE) in Shergotty, and the NWA 7533 clasts (except for one monzonitic sample) have compositions overlapping with this range. The total δ⁹⁴Zr_IPGP-Zr range of <0.1 ‰ indicates that the formation of the mafic martian samples was not associated with significant mass dependent Zr isotope fractionation. Hence, we suggest that the mean isotope composition of these samples reflects the best estimate of the martian mantle δ⁹⁴Zr_IPGP-Zr composition of 0.062 ± 0.043 ‰ (2SD, n = 37), which is indistinguishable from the current best estimate of Earth's mantle (δ⁹⁴Zr_IPGP-Zr = 0.40 ± 0.44 ‰, 2SD, n = 72).

An evolved monzonitic clast from NWA 7533, on the other hand, records an extreme δ⁹⁴Zr_IPGP-Zr value of 0.362 ± 0.008 ‰ (2SE). This isotopically heavy signature likely reflects fractional crystallisation of ilmenite, baddeleyite, and/or zircon. Lastly, we suggest that the limited δ⁹⁴Zr variability observed for the NWA 7533 basaltic igneous clasts, which contain a puzzling abundance of zircon considering their zircon-undersaturated bulk compositions, reflects late-stage zircon saturation in pockets of residual melt.

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火星地幔稳定的锆同位素组成

我们报告高精度稳定的Zr同位素数据为广泛选择的火星陨石使用双钉法。所调查的样品包括长辉石岩、nakhlite、单一辉石岩和来自西北非洲（NWA） 7533风化角砾岩陨石的几个碎屑。这些样品主要是基性成分，它们表现出有限的，但可分解的，稳定的Zr同位素组成。具体来说，SNC陨石记录的δ94ZrIPGP-Zr的组成范围从焦法019的0.021±0.003‰（2SE）扩展到舍戈蒂的0.093±0.018‰（2SE）， NWA 7533碎屑（除一个二长岩样品外）的组成与此范围重叠。δ94ZrIPGP-Zr的总δ94ZrIPGP-Zr为0.1‰，表明基性火星样品的形成与明显的质量依赖的Zr同位素分馏无关。因此，我们认为这些样品的平均同位素组成反映了火星地幔δ94ZrIPGP-Zr组成的最佳估计为0.062±0.043‰（2SD, n = 37），与目前地球地幔的最佳估计（δ94ZrIPGP-Zr = 0.40±0.44‰，2SD, n = 72）没有区别。NWA 7533演化二长岩的δ94ZrIPGP-Zr极值为0.362±0.008‰（2SE）。这种重同位素特征可能反映了钛铁矿、坏辉石和/或锆石的分异结晶。最后，我们认为NWA 7533玄武质火成岩碎屑的δ94Zr有限变率反映了后期残余熔体中锆石的饱和状态，考虑到它们的锆石欠饱和体组成，锆石含量令人困惑。

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来源期刊

Chemical Geology 地学-地球化学与地球物理

CiteScore

7.20

自引率

10.30%

发文量

374

审稿时长

3.6 months

期刊介绍： Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry. The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry. Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry. The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.