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首页> 外文期刊>Contributions to Mineralogy and Petrology >Phase relations and formation of sodium-rich majoritic garnet in the system Mg3Al2Si3O12–Na2MgSi5O12 at 7.0 and 8.5 GPa
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Phase relations and formation of sodium-rich majoritic garnet in the system Mg3Al2Si3O12–Na2MgSi5O12 at 7.0 and 8.5 GPa

机译：Mg 3 Al 2 Si 3 O 12 –体系中富钠的石榴石石榴石的相关系和形成Na 2 MgSi 5 O 12 在7.0和8.5 GPa下

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摘要

The pseudo-binary system Mg3Al2Si3O12–Na2MgSi5O12 modelling the sodium-bearing garnet solid solutions has been studied at 7 and 8.5 GPa and 1,500–1,950°C. The Na-bearing garnet is a liquidus phase of the system up to 60 mol% Na2MgSi5O12 (NaGrt). At higher content of NaGrt in the system, enstatite (up to ∼80 mol%) and then coesite are observed as liquidus phases. Our experiments provided evidence for a stable sodium incorporation in garnet (0.3–0.6 wt% Na2O) and its control by temperature and pressure. The highest sodium contents were obtained in experiments at P = 8.5 GPa. Near the liquidus (T = 1,840°C), the equilibrium concentration of Na2O in garnet is 0.7–0.8 wt% (∼6 mol% Na2MgSi5O12). With the temperature decrease, Na concentration in Grt increases, and the maximal Na2MgSi5O12 content of ∼12 mol% (1.52 wt% Na2O) is gained at the solidus of the system (T = 1,760°С). The data obtained show that most of natural diamonds, with inclusions of Na-bearing garnets usually containing 1 wt% Na2O) may crystallize at a pressure range of 7.0–8.5 GPa. However the upper pressure limit for the formation of naturally occurring Na-bearing garnets is restricted by the eclogite/garnetite bulk composition.
机译：伪二元体系Mg 3 Al 2 Si 3 O 12 –Na 2 MgSi 5 O 12 模拟含钠石榴石固溶体的温度分别为7和8.5 GPa，以及1,500–1,950°C。含钠石榴石是系统的液相线，最高含量为60 mol％Na 2 MgSi 5 O 12 （NaGrt）。在系统中较高的NaGrt含量时，观察到了顽辉石（至多80 mol％），然后是绢云母为液相。我们的实验提供了在石榴石中稳定掺入钠（0.3–0.6 wt％Na 2 O）及其受温度和压力控制的证据。在实验中，P = 8.5 GPa时，钠含量最高。在液相线附近（T = 1,840°C），石榴石中Na 2 O的平衡浓度为0.7–0.8 wt％（〜6 mol％Na 2 MgSi 5 O 12 ）。随着温度的降低，Grt中的Na浓度增加，并且最大的Na 2 MgSi 5 O 12 含量约为-12 mol％（1.52 wt在系统的固相线（T = 1,760°С）处获得％Na 2 O）。获得的数据表明，大多数天然钻石，包括通常含1 wt％Na 2 O的含钠石榴石，都可以在7.0–8.5 GPa的压力范围内结晶。但是，天然锂榴石/榴辉石块的组成限制了天然形成的含钠石榴石的形成的压力上限。

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