Petrogenesis and chronology of lunar meteorite Northwest Africa 4472: A KREEPy regolith breccia from the Moon
Petrogenesis and chronology of lunar meteorite Northwest Africa 4472: A KREEPy regolith breccia from the Moon
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DOI：
10.1016/j.gca.2011.02.018
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发表时间：
2011-05
影响因子：
5
通讯作者：
K. Joy;R. Burgess;R. Hinton;V. Fernandes;I. Crawford;A. Kearsley;A. Irving
中科院分区：
文献类型：
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作者：
K. Joy;R. Burgess;R. Hinton;V. Fernandes;I. Crawford;A. Kearsley;A. Irving
西北部非洲(NWA)4472是一颗多重的月球风化陨石。该样品富含Kreep(高浓度的钾、稀土元素和磷)，并由一系列不同种类的岩屑和矿物碎片组成。这些碎屑和矿物碎片来自一系列月球岩石类型，包括月球高镁系列、高碱性系列、克里普玄武岩、母质玄武岩和各种撞击坑环境。NWA4472富含Kreep的性质表明，样品是从月球近侧Procellarum Kreep地体的风化岩中喷出的，我们利用月球勘探者伽马射线遥感数据表明，该陨石最类似于(也最有可能来自)英云撞击盆地附近的风化岩。NWA4472个磷酸盐相的U-Pb值和PbPb值表明，角砾岩中含有与早期Kreep驱动岩浆活动有关的前玄武岩(4.35Ga)。一些较年轻的磷酸盐U-铅和铅-铅年龄很可能表明了3.9-4Ga的撞击重置事件，这与月球上盆地形成的建议时间一致。我们的研究还表明，NWA4472采样的撞击熔体和玻璃具有富碱、不相容的微量元素富集型(高Sc，低Rb/Th比，低K)的成分特征，与典型的阿波罗高K Kreep无关，也与Kreepy月球陨石Sayh al Uhaymir(SAU)169的采样无关。这提供了证据，证明月球上有许多富含克里普的原岩来源。
Northwest Africa (NWA) 4472 is a polymict lunar regolith meteorite. The sample is KREEP-rich (high concentrations of potassium, rare earth elements and phosphorus) and comprises a heterogeneous array of lithic and mineral fragments. These clasts and mineral fragments were sourced from a range of lunar rock types including the lunar High Magnesian Suite, the High Alkali Suite, KREEP basalts, mare basalts and a variety of impact crater environments. The KREEP-rich nature of NWA 4472 indicates that the sample was ejected from regolith on the nearside of the Moon in the Procellarum KREEP Terrane and we have used Lunar Prospector gamma-ray remote sensing data to show that the meteorite is most similar to (and most likely sourced from) regoliths adjacent to the Imbrium impact basin. U–Pb and Pb–Pb age dates of NWA 4472 phosphate phases reveal that the breccia has sampled Pre-Nectarian (4.35Ga) rocks related to early episodes of KREEP driven magmatism. Some younger phosphate U–Pb and Pb–Pb age dates are likely indicative of impact resetting events at 3.9–4Ga, consistent with the suggested timing of basin formation on the Moon. Our study also shows that NWA 4472 has sampled impact melts and glass with an alkali-depleted, incompatible trace element-rich (high Sc, low Rb/Th ratios, low K) compositional signature not related to typical Apollo high-K KREEP, or that sampled by KREEPy lunar meteorite Sayh al Uhaymir (SaU) 169. This provides evidence that there are numerous sources of KREEP-rich protoliths on the Moon.