Calcium‐aluminum‐rich inclusions (CAIs) are the first solid materials formed in the solar nebula. Among them, ultrarefractory inclusions are very rare. In this study, we report on the mineralogical features and oxygen isotopic compositions of minerals in a new ultrarefractory inclusion CAI 007 from the CV3 chondrite Northwest Africa (NWA) 3118. The CAI 007 inclusion is porous and has a layered (core–mantle–rim) texture. The core is dominant in area and mainly consists of Y‐rich perovskite and Zr‐rich davisite, with minor refractory metal nuggets, Zr,Sc‐rich oxide minerals (calzirtite and tazheranite), and Fe‐rich spinel. The calzirtite and tazheranite are closely intergrown, probably derived from a precursor phase due to thermal metamorphism on the parent body. The refractory metal nuggets either exhibit thin exsolution lamellae of Fe,Ni‐dominant alloy in Os,Ir‐dominant alloy or are composed of Os,Ir,Ru,Fe‐alloy and Fe,Ni,Ir‐alloy with troilite, scheelite, gypsum, and molybdenite. The later four phases are apparently secondary minerals. The Zr,Sc,Y‐rich core is surrounded by a discontinuous layer of closely intergrown hibonite and spinel. The CAIs are rimmed by Fe‐rich spinel and Al‐rich diopside. Perovskite has high concentrations of the most refractory rare earth elements (REEs) but is relatively depleted in the moderately refractory and volatile REEs, consistent with the ultrarefractory REE pattern. Based on this unusual Zr,Sc,Y‐rich mineral assemblage, the layered distribution in CAI 007, and the REE concentrations in perovskite, we suggest that CAI 007 is an ultrarefractory inclusion of condensation origin. In CAI 007, hibonite, spinel, and probably Al‐rich diopside are ¹⁶O‐rich (Δ¹⁷O ~–22‰) whereas perovskite and davisite are ¹⁶O‐poor (Δ¹⁷O ~–3‰). Such oxygen isotope heterogeneity suggests that the UR inclusion formed in the various degrees of ¹⁶O‐rich nebular setting or was originally ¹⁶O‐rich and then experienced oxygen isotope exchange with ¹⁶O‐poor fluid on the CV3 chondrite parent body.

中文翻译：

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西北非 3118 CV3 球粒陨石中一种新的超难熔包裹体的矿物学和氧同位素研究

富含钙铝包裹体（CAI）是太阳星云中最早形成的固体物质。其中，超难熔夹杂物非常少见。在这项研究中，我们报告了来自 CV3 球粒陨石西北非 (NWA) 3118 的新超难熔包裹体 CAI 007 中矿物的矿物学特征和氧同位素组成。 ） 质地。岩心在面积上占优势，主要由富 Y 钙钛矿和富 Zr 闪锌矿组成，少量难熔金属块、富 Zr、Sc 氧化物矿物（钙钛矿和 tazheranite）和富铁尖晶石。Calzirtite 和 tazheranite 紧密共生，可能源自母体热变质作用的前体相。难熔金属块要么表现出较薄的 Fe 出溶片层，Os,Ir-dominant 合金中的Ni-主导合金或由Os,Ir,Ru,Fe-合金和Fe,Ni,Ir-合金与硫钛矿、白钨矿、石膏和辉钼矿组成。后四个阶段显然是次生矿物。富含 Zr,Sc,Y 的核被紧密共生的黑曜石和尖晶石的不连续层包围。CAI 的边缘是富铁尖晶石和富铝透辉石。钙钛矿具有高浓度的最难熔的稀土元素 (REE)，但在中等难熔和易挥发的 REE 中相对贫乏，这与超难熔稀土元素模式一致。基于这种不寻常的富含 Zr、Sc、Y 的矿物组合、CAI 007 中的层状分布以及钙钛矿中的 REE 浓度，我们认为 CAI 007 是凝结成因的超难熔夹杂物。CAI 007、黑曜石、尖晶石、可能富含铝的透辉石富含 ¹⁶O（Δ¹⁷O ~–22‰），而钙钛矿和菱镁矿则缺乏 ¹⁶O（Δ¹⁷O ~–3‰）。这种氧同位素异质性表明 UR 包裹体在不同程度的富含 ¹⁶O 的星云环境中形成，或者最初富含 ¹⁶O，然后与 CV3 球粒陨石母体上的 ¹⁶O 贫流体发生氧同位素交换。