| Popis: |
Alkali-rich carbonate melts are found as inclusions in magmatic minerals, mantle xenoliths, and diamonds from kimberlites and lamproites worldwide. However, the depth of their origin and bulk melt composition remains unclear. Here, we studied quench products of K-Ca-Mg carbonate melt at 3 and 6 GPa. The following carbonates were detected at 3 GPa: K2CO3, K2Ca(CO3)2 bütschliite (R3¯2/m), o-K2Ca3(CO3)4 (P212121), K2Ca2(CO3)3 (R3), K2Mg(CO3)2 (R3¯m), Mg-bearing calcite, dolomite, and magnesite. At 6 GPa, the variety of quench carbonate phases includes K2CO3, K2Ca(CO3)2 bütschliite (R3¯2/m), d-K2Ca3(CO3)4 (Pnam), K2Mg(CO3)2 (R3¯m), aragonite, Mg-bearing calcite, dolomite, and magnesite. The data obtained indicate that alkali-bearing carbonate melts quench to the alkaline earth and double carbonates that are thermodynamically stable at quenching pressure and can be used as markers reflecting the pressure of their entrapment. Further, in this study, we established the fields of melt compositions corresponding to the distinct quench assemblages of carbonate minerals, which can be used for the reconstruction of the composition of carbonatitic melts entrapped by mantle minerals. |
