The petrologic and oxygen isotopic characteristics of calcium‐aluminum‐rich inclusions (CAIs) in CO chondrites were further constrained by studying CAIs from six primitive CO3.0‐3.1 chondrites, including two Antarctic meteorites (DOM 08006 and MIL 090010), three hot desert meteorites (NWA 10493, NWA 10498, and NWA 7892), and the Colony meteorite. The CAIs can be divided into hibonite‐bearing inclusions (spinel‐hibonite spherules, monomineralic grains, hibonite‐pyroxene microspherules, and irregular/nodular objects), grossite‐bearing inclusions (monomineralic grains, grossite‐melilite microspherules, and irregular/nodular objects), melilite‐rich inclusions (fluffy Type A, compact type A, monomineralic grains, and igneous fragments), spinel‐pyroxene inclusions (fluffy objects resembling fine‐grained spinel‐rich inclusions in CV chondrites and nodular/banded objects resembling those in CM chondrites), and pyroxene‐anorthite inclusions. They are typically small (98.4 ± 54.4 µm, 1SD) and comprise 1.54 ± 0.43 (1SD) area% of the host chondrites. Melilite in the hot desert and Colony meteorites was extensively replaced by a hydrated Ca‐Al‐silicate during terrestrial weathering and converted melilite‐rich inclusions into spinel‐pyroxene inclusions. The CAI populations of the weathered COs are very similar to those in CM chondrites, suggesting that complete replacement of melilite by terrestrial weathering, and possibly parent body aqueous alteration, would make the CO CAIs CM‐like, supporting the hypothesis that CO and CM chondrites derive from similar nebular materials. Within the CO3.0‐3.1 chondrites, asteroidal alteration significantly resets oxygen isotopic compositions of CAIs in CO3.1 chondrites (∆¹⁷O: −25 to −2‰) but left those in CO3.0‐3.05 chondrites mostly unchanged (∆¹⁷O: −25 to −20‰), further supporting the model whereby thermal metamorphism became evident in CO chondrites of petrologic type ≥3.1. The resistance of CAI minerals to oxygen isotope exchange during thermal metamorphism follows in the order: melilite + grossite < hibonite + anorthite < spinel + diopside + forsterite. Meanwhile, terrestrial weathering destroys melilite without changing the chemical and isotopic compositions of melilite and other CAI minerals.

中文翻译：

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原始CO3.0-3.1球粒陨石中富含钙铝夹杂物的岩石学和氧同位素组成

通过研究6种原始CO3.0-3.1球粒陨石的CAI，进一步限制了CO球粒陨石中钙-铝-富集夹杂物的岩石学和氧同位素特征，包括两个南极陨石（DOM 08006和MIL 090010），三个热沙漠陨石（NWA 10493，NWA 10498和NWA 7892）以及殖民地陨石。CAI可以分为含辉石的夹杂物（尖晶石-辉石球体，单矿物颗粒，辉石-py微球和不规则/球状物体），含钙石的夹杂物（单矿物晶粒，钙铁矿-沸石微球和不规则/球状物体） ，富含陨石的夹杂物（蓬松的A型，致密的A型，单矿物颗粒和火成岩碎片），尖晶石-辉石夹杂物（蓬松的物体，类似于CV球粒陨石中的细晶尖晶石富集夹杂物，而球状/带状物体，类似于CM的球粒陨石），辉石-钙长石夹杂物。它们通常很小（98.4±54.4 µm，1SD），占主体球粒陨石面积的1.54±0.43（1SD）％。在陆地风化过程中，炎热的沙漠中的陨石和集落陨石被水合的Ca-Al-硅酸盐广泛取代，并将富含陨石的包裹体转变为尖晶石-rox夹杂物。风化CO的CAI种群与CM球粒陨石的CAI种群非常相似，这表明陆地风化作用完全取代陨石，并可能使母体水体发生变化，会使CO CAI变成CM，支持CO和CM球粒陨石的假说。来源于类似的神经质。¹⁷ O：−25至-2‰），但保留了CO3.0‐3.05球粒陨石中的大部分不变（∆ ¹⁷ O：−25至−20‰），进一步支持了热变质在岩石类型的CO球粒中明显的模型≥3.1。在热变质过程中，CAI矿物对氧同位素交换的抵抗力顺序为：陨石+岗石<锂铁矿+钙长石<br /> <尖晶石+透辉石+镁橄榄石。同时，陆地风化破坏了陨石，而不会改变陨石和其他CAI矿物的化学和同位素组成。