Mineralogical and oxygen isotopic study of a new ultrarefractory inclusion in the Northwest Africa 3118 CV3 chondrite
Mineralogical and oxygen isotopic study of a new ultrarefractory inclusion in the Northwest Africa 3118 CV3 chondrite
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DOI：
10.1111/maps.13575
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发表时间：
2020-10
影响因子：
2.2
通讯作者：
Y. Xiong;A. Zhang;N. Kawasaki;Chi Ma;N. Sakamoto;Jia‐Ni Chen;L. Gu;H. Yurimoto
中科院分区：
文献类型：
--
作者：
Y. Xiong;A. Zhang;N. Kawasaki;Chi Ma;N. Sakamoto;Jia‐Ni Chen;L. Gu;H. Yurimoto
富含钙铝的包裹体（CAI）是太阳星云中形成的第一个固体材料。其中，超耐火夹杂物非常罕见。在这项研究中，我们报告了来自 CV3 球粒陨石西北非 (NWA) 3118 的新型超难熔包裹体 CAI 007 中矿物的矿物学特征和氧同位素组成。CAI 007 包裹体是多孔的，具有层状（核-幔-边缘）结构。核心面积占主导地位，主要由富Y钙钛矿和富Zr菱镁矿组成，少量难熔金属块、富Zr、Sc氧化物矿物（钙锆石和泰哲石）和富铁尖晶石。方解石和泰泽瑞石紧密共生，可能源自母体热变质作用的前体相。难熔金属块要么在 Os,Ir 主导合金中表现出 Fe,Ni 主导合金的薄析出片层，要么由 Os,Ir,Ru,Fe 合金和 Fe,Ni,Ir 合金与陨石、白钨矿、石膏和辉钼矿组成。后面的四相显然是次生矿物。富含 Zr、Sc、Y 的核心被紧密共生的黑铝矿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稀土元素 (REE)，但中等难熔和挥发性 REE 相对贫乏，这与超难熔 REE 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 是一种凝结成因的超难熔包裹体。在 CAI 007 中，黑铝石、尖晶石和可能富铝透辉石富含 16O（Δ17O ~–22‰），而钙钛矿和菱镁矿则贫 16O（Δ17O ~–3‰）。这种氧同位素异质性表明UR包裹体是在不同程度的富含16O的星云环境中形成的，或者最初是富含16O的，然后在CV3球粒陨石母体上与贫16O的流体进行了氧同位素交换。
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.