Ureilites are carbon‐rich ultramafic achondrites that have been heated above the silicate solidus, do not contain plagioclase, and represent the melting residues of an unknown planetesimal (i.e., the ureilite parent body, UPB). Melting residues identical to pigeonite‐olivine ureilites (representing 80% of ureilites) have been produced in batch melting experiments of chondritic materials not depleted in alkali elements relative to the Sun’s photosphere (e.g., CI, H, LL chondrites), but only in a relatively narrow range of temperature (1120 ºC–1180 ºC). However, many ureilites are thought to have formed at higher temperature (1200 ºC–1280 ºC). New experiments, described in this study, show that pigeonite can persist at higher temperature (up to 1280 ºC) when CI and LL chondrites are melted incrementally and while partial melts are progressively extracted. The melt productivity decreases dramatically after the exhaustion of plagioclase with only 5–9 wt% melt being generated between 1120 ºC and 1280 ºC. The relative proportion of pyroxene and olivine in experiments is compared to 12 ureilites, analyzed for this study, together with ureilites described in the literature to constrain the initial Mg/Si ratio of the UPB (0.98–1.05). Experiments are also used to develop a new thermometer based on the partitioning of Cr between olivine and low‐Ca pyroxene that is applicable to all ureilites. The equilibration temperature of ureilites increases with decreasing Al₂O₃ and Wo contents of pyroxene and decreasing bulk REE concentrations. The UPB melted incrementally, at different f O₂, and did not cool significantly (0 ºC–30 ºC) prior to its disruption. It remained isotopically heterogenous, but the initial concentration of major elements (SiO₂, MgO, CaO, Al₂O₃, alkali elements) was similar in the different mantle reservoirs.

中文翻译：

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在尿素石母体中的增量熔化：初始组成，熔化温度和熔化物组成

尿素石是富含碳的超镁铁质的陨石，已被加热到硅酸盐固相线以上，不含斜长石，并且代表未知行星的熔融残余物（即，尿素石母体UPB）。在不对相对于太阳光球的碱元素（例如，CI，H，LL球粒陨石）消耗碱元素的情况下，对软骨材料进行批熔融实验时，产生了与皂石-橄榄石沸石相同的熔融残留物（占80％的沸石）。温度范围相对较窄（1120 ºC–1180ºC）。但是，许多尿素岩被认为是在较高的温度（1200 ºC–1280ºC）下形成的。本研究中描述的新实验 结果表明，当CI和LL球粒陨石逐渐融化并逐渐提取部分熔体时，皂石可以在更高的温度下（最高1280ºC）持续存在。斜长石耗尽后，熔体生产率急剧下降，在1120℃至1280℃之间仅产生5-9 wt％的熔体。将实验中辉石和橄榄石的相对比例与本研究进行了分析的12个尿素石进行比较，并结合文献中描述的尿素石来限制UPB的初始Mg / Si比（0.98-1.05）。实验还用于开发基于橄榄石和低钙辉石之间的Cr分配的新型温度计，该温度计适用于所有尿素。尿素的平衡温度随着Al的减少而增加 斜长石耗尽后，熔体生产率急剧下降，在1120℃至1280℃之间仅产生5-9 wt％的熔体。将本研究中分析的辉石和橄榄石的相对比例与本研究中分析的12种尿素进行比较，并结合文献中描述的尿素来限制UPB的初始Mg / Si比（0.98-1.05）。实验还用于开发基于橄榄石和低钙辉石之间的Cr分配的新型温度计，该温度计适用于所有尿素。尿素的平衡温度随着Al的减少而增加 斜长石耗尽后，熔体生产率急剧下降，在1120℃至1280℃之间仅产生5-9 wt％的熔体。将实验中辉石和橄榄石的相对比例与本研究进行了分析的12个尿素石进行比较，并结合文献中描述的尿素石来限制UPB的初始Mg / Si比（0.98-1.05）。实验还用于开发基于橄榄石和低钙辉石之间的Cr分配的新型温度计，该温度计适用于所有尿素。尿素的平衡温度随着Al的减少而增加 结合文献中描述的尿素来限制UPB的初始Mg / Si比（0.98–1.05）。实验还用于开发基于橄榄石和低钙辉石之间的Cr分配的新型温度计，该温度计适用于所有尿素。尿素的平衡温度随着Al的减少而增加 结合文献中描述的尿素来限制UPB的初始Mg / Si比（0.98–1.05）。实验还用于开发基于橄榄石和低钙辉石之间的Cr分配的新型温度计，该温度计适用于所有尿素。尿素的平衡温度随着Al的减少而增加辉石的₂ O ₃和Wo含量和整体REE浓度降低。UPB在不同的f O _2下逐渐熔化，在破裂之前并未显着冷却（0 ºC–30ºC）。它保持同位素异质性，但在不同的地幔储层中，主要元素（SiO ₂，MgO，CaO，Al ₂ O ₃，碱金属元素）的初始浓度相似。