Abstract Compositional ranges of carbonate melt s stable under P-T conditions corresponding to the base of subcontinental lithospheric mantle (SCLM) are limited by alkali-rich near-eutectic compositions. In the present work, we investigated the interaction of such melts with the natural eclogite of Group A. It was found that the interaction is accompanied by decreasing Ca# in the melt (L) and increasing Ca# in garnet (Grt) according to the reaction: 3CaCO3 (L) + Mg3Al2Si3O12 (Grt) = 3MgCO3 (Mgs and/or L) + Ca3Al2Si3O12 (Grt), where Mgs is magnesite. The interaction with the Na-Ca-Mg-Fe carbonate melt increases amount of jadeite component in clinopyroxene (Cpx) consuming Al2O3 from garnet and Na2O from the melt according to the reaction: Na2CO3 (L) + CaCO3 (L) + 2Mg3Al2Si3O12 (Grt) + 2CaMgSi2O6 (Cpx) = 2NaAlSi2O6 (Cpx) + Ca3Al2Si3O12 (Grt) + 2MgCO3 (Mgs, L) + 3Mg2SiO4 (Ol). As a result, garnet and omphacite compositions evolve from eclogite Group A to eclogite Group B. A byproduct of the reaction is olivine (Ol), which may explain the formation of inclusions of “mixed” eclogite (garnet + omphacite) and peridotite (olivine) paragenesis in lithospheric diamonds. The interaction with the K-Ca-Mg-Fe carbonate melt increases the K2O content in clinopyroxene to 0.5–1.2 wt%, while the Na2O content lowers to 0.3 wt%. The following range of carbonatite melt compositions can be in equilibrium with eclogite at the base of SCLM (1100–1200 °C and 6 GPa): 18(Na0.97K0.03)2CO3∙82(Ca0.63Mg0.30Fe0.07)CO2–42(Na0.97K0.03)2CO3∙58(Ca0.46Mg0.45Fe0.09)CO2. Our results also suggest that the partial melting of ‘dry’ carbonated eclogite, if any, at 1100 °C and 6 GPa yields the formation of a carbonate melt with the following composition (mol%) 25(Na0.96K0.04)2CO3∙75(Ca0.64Mg0.31Fe0.05)CO2, corresponding to 18–27 wt% Na2O in the melt on a volatile-free basis.

中文翻译：

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在 6 GPa 和 1100–1200 °C 时碳酸盐熔体与天然榴辉岩的相互作用：对次大陆岩石圈地幔交代熔体成分的影响

摘要 对应于次大陆岩石圈地幔 (SCLM) 基底的 PT 条件下稳定的碳酸盐熔体的成分范围受到富碱近共晶成分的限制。在目前的工作中，我们研究了这种熔体与 A 组天然榴辉岩的相互作用。发现这种相互作用伴随着熔体 (L) 中 Ca# 的减少和石榴石中 Ca# (Grt) 的增加，根据反应：3CaCO3 (L) + Mg3Al2Si3O12 (Grt) = 3MgCO3 (Mgs 和/或 L) + Ca3Al2Si3O12 (Grt)，其中 Mgs 是菱镁矿。根据反应，与 Na-Ca-Mg-Fe 碳酸盐熔体的相互作用增加了单斜辉石 (Cpx) 中硬玉组分的量，消耗了石榴石中的 Al2O3 和熔体中的 Na2O：Na2CO3 (L) + CaCO3 (L) + 2Mg3Al2Si3O12 (Grt) + 2CaMgSi2O6 (Cpx) = 2NaAlSi2O6 (Cpx) + Ca3Al2Si3O12 (Grt) + 2MgCO3 (Mgs, L) + 3Mg2SiO4 (Ol)。因此，石榴石和绿辉石组成从榴辉岩 A 组演变为榴辉岩 B 组。反应的副产物是橄榄石 (Ol)，这可以解释“混合”榴辉岩（石榴石 + 绿辉石）和橄榄岩（橄榄石）包裹体的形成) 岩石圈金刚石中的共生作用。与 K-Ca-Mg-Fe 碳酸盐熔体的相互作用使单斜辉石中的 K2O 含量增加到 0.5-1.2 wt%，而 Na2O 含量降低到 0.3 wt%。以下范围的碳酸岩熔体成分可以与 SCLM 底部的榴辉岩平衡（1100-1200 °C 和 6 GPa）： 18(Na0.97K0.03)2CO3∙82(Ca0.63Mg0.30Fe0.07)CO2 –42(Na0.97K0.03)2CO3∙58(Ca0.46Mg0.45Fe0.09)CO2。