Petrologic investigations of martian meteorite Northwest Africa (NWA) 13227 indicate it is an olivine-gabbroic shergottite, a relatively new shergottite group, which differs from previously described gabbroic shergottites due to relatively high quantities of olivine. NWA 13227 is comprised of phenocrystic, oscillatory-zoned pyroxene and olivine, set in a matrix of maskelynite, Fe-Cr-Ti oxides, phosphates, and sulfides. It displays gabbroic and poikilitic textures in 2D from back-scattered electron images, and in 3D from X-ray Computed Tomography (XCT) imaging, suggesting affinities to both poikilitic and gabbroic shergottites. Measured εHf and εNd values of bulk rock (-19.7 and −5.9, respectively) and its chondrite-normalized La/Yb ratio of 1.13 indicate the specimen is derived from a mantle reservoir relatively enriched in incompatible trace elements and is similar to that which produced most ‘enriched shergottites.’ Based on the Ti/Al ratio of pyroxene, phosphorous zoning in olivine, and minor components in phosphates and oxides, we infer that NWA 13227 began crystallizing under reducing conditions of QFM–2.6 and temperatures of ∼ 1100 °C, consistent with conditions in Mars’ lower crust/upper mantle. The sample finished crystallizing at or near the surface under redox conditions between QFM–0.5 to QFM–0.1 and temperatures of ∼ 850 °C. The volatile element compositions in apatite indicate that NWA 13227 experienced degassing during the last stages of crystallization. The timing of crystallization is estimated at 225 Ma ± 50 Ma using a Lu-Hf and Sm-Nd source versus age model.

中文翻译：

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新型侵入性角辉岩的岩石成因：橄榄石辉长岩西北非 13227

对火星陨石西北非 (NWA) 13227 的岩石学研究表明，它是橄榄石-辉长辉长辉长岩，是一个相对较新的辉长辉长岩群，由于橄榄石含量相对较高，与之前描述的辉长辉长辉长岩不同。 NWA 13227 由斑晶、振荡分区辉石和橄榄石组成，镶嵌在马氏沸石、Fe-Cr-Ti 氧化物、磷酸盐和硫化物基质中。它显示了来自背散射电子图像的 2D 辉长岩和异辉长岩纹理，以及来自 X 射线计算机断层扫描 (XCT) 成像的 3D 辉长岩和异辉长岩纹理，表明与异辉长岩和辉长岩辉长岩都有亲缘关系。大块岩石的 εHf 和 εNd 测量值（分别为 -19.7 和 -5.9）及其球粒陨石归一化的 La/Yb 比值为 1.13，表明该样本源自不相容微量元素相对富集的地幔储层，与产生的地幔储层相似。大多数“丰富的谢尔戈蒂人”。根据辉石的 Ti/Al 比、橄榄石中的磷分带以及磷酸盐和氧化物中的少量成分，我们推断 NWA 13227 在 QFM–2.6 的还原条件和~ 1100 °C 的温度下开始结晶，与火星上的条件一致' 下地壳/上地幔。在 QFM–0.5 至 QFM–0.1 之间的氧化还原条件和约 850 °C 的温度下，样品在表面或表面附近完成结晶。磷灰石中的挥发性元素组成表明 NWA 13227 在结晶的最后阶段经历了脱气。使用 Lu-Hf 和 Sm-Nd 源与年龄模型估计结晶时间为 225 Ma ± 50 Ma。