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首页> 外文期刊>Contributions to Mineralogy and Petrology >Phase relations of carbonate-bearing eclogite assemblages from 2.5 to 5.5 GPa: implications for petrogenesis of carbonatites
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Phase relations of carbonate-bearing eclogite assemblages from 2.5 to 5.5 GPa: implications for petrogenesis of carbonatites

机译：2.5至5.5 GPa的含碳酸盐榴辉岩组合的相关系：对碳酸盐岩成岩作用的影响

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摘要

We have experimentally investigated the phase and melting relations of garnet + clinopyroxene + carbonate assemblages at 2.5-5.5 GPa, to assess the feasibility of carbonated eclogite as a source for some crustally emplaced carbonatites. The solidus of our composition was at ≈1,125 ℃ at 2.5 GPa, ≈1,225 ℃ at 3.5 GPa and ≈1,310 ℃ at 5.0 GPa. Melts were sodic calcio-dolomitic carbonatites, and were markedly more calcic than the dolomitic melts produced by partial melting of carbonated peridotite. Na contents of the experimental carbonatites decreased with increasing pressure when compared at similar degrees of melting, and SiO_2 contents increased with degree of melting. Experiments on a second composition with enhanced Na_2O demonstrated its strong effect in lowering melting temperatures in carbonate eclogite. Natural carbonated eclogite bodies in the peridotitic upper mantle will have a range of solidus temperatures. In many cases, carbonate will be molten in the upper ≥250 km. Carbonate melt would segregate from its source eclogite at very low melt fractions and infiltrate surrounding peridotitic wall rock. This would result in metasomatic enrichment of the peridotitic wall rock, but its exact nature will depend on the relative P-T positions of the eclogite + CO_2 and peridotite + CO_2 solidii. As a result of these inevitable metasomatic interactions, it is considered unlikely that carbonatite melts derived from carbonated eclogite in the upper mantle could be emplaced into the crust unmodified. However, they may have a role in metasomatically enriching and carbonating parts of the upper mantle, producing sources suitable for subsequent production of silica undersaturated silicate liquids and carbonatites ultimately emplaced in the crust.
机译：我们已经通过实验研究了石榴石+斜py石+碳酸盐组合物在2.5-5.5 GPa的相和熔融关系，以评估碳酸钙榴石作为某些地壳碳酸盐的来源的可行性。我们的组合物的固相线在2.5 GPa时约为≈1,125℃，在3.5 GPa时约为1,225℃，在5.0 GPa时约为1,310℃。熔体是苏打钙质-白云岩质碳酸盐岩，比起碳酸化橄榄岩部分熔融产生的白云质熔岩，钙质明显更多。在相似的熔融度下，实验碳酸盐的Na含量随压力的增加而降低，而SiO_2含量随熔融度的增加而升高。对具有增强的Na_2O的第二种组合物进行的实验表明，它具有降低碳酸盐榴辉岩熔融温度的强大作用。橄榄岩上地幔中的天然碳酸榴辉岩体将具有一定范围的固相线温度。在许多情况下，碳酸盐将在≥250km的上部熔融。碳酸盐熔体会以极低的熔体含量从其来源榴辉岩中分离出来，并渗入周围的橄榄岩围岩中。这将导致橄榄岩围岩的交代富集，但其确切性质将取决于榴辉岩+ CO_2和橄榄岩+ CO_2固相的相对P-T位置。这些不可避免的交代作用的结果是，人们认为上地幔中碳酸盐榴辉岩衍生的碳酸盐熔体不可能原封不动地进入地壳。但是，它们可能在交代富集和碳化上地幔的部分中发挥作用，产生了适合于随后生产二氧化硅欠饱和硅酸盐液体和最终置于地壳中的碳酸盐的来源。

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