The breakdown of diopside to (Ca, Mg)SiO3 perovskite-(Mg, Ca, Fe)SiO3 glass-(Mg, Ca)SiO3 glass-(Mg, Ca)SiO3 majorite in a melt vein the Suizhou L6 chondrite

The Suizhou meteorite is a heavily shocked and melted vein-containing L6 chondrite. It contains a minor amount of diopside with a (Ca0.419Mg0.466Fe0.088)SiO3 composition, and a shock-metamorphosed diopside grain associated with ringwoodite and lingunite was found in a melt vein of this meteorite. Our electron microprobe, transmission electron microscopic and Raman spectroscopic analyses revealed four silicate phases with different compositions and structures inside this shock-metamorphosed diopside grain, termed phase A, B, C and D in this paper. Phase A is identified as orthorhombic (Ca0.663Mg0.314)SiO3-perovskite which is closely associated with phase B, the vitrified (Mg0.642Ca0.290Fe0.098)SiO3 perovskite. Phase D is assigned to be (Mg0.578Ca0.414)SiO3 majorite which is associated with phase C, the vetrified Ca-rich Mg-perovskite with a (Mg0.853Ca0.167)SiO3 composition. Based on high-pressure and high-temperature experiments, the diopside grain in the melt vein of the Suizhou meteorite would have experienced a P-T regime of 20-24 GPa and 1800 - > 2000 degrees C. Such P-T conditions are high enough for the decomposition of the diopside and the formation of four different silicate phases. The orthorhombic (Ca0.663Mg0.314)SiO3 perovskite found in the Suizhou L6 chondrite might be considered as the third lower-mantle silicate mineral after bridgmanite and davemaoite after the detailed analyses of its crystal structure and physical properties being completed.

Automated summary

This article describes a heavily shocked and melted Suizhou meteorite that contains a minor amount of diopside. A shock-metamorphosed diopside grain associated with ringwoodite and lingunite was found inside a melt vein of this meteorite. Through various analyses, four silicate phases named A, B, C, and D were identified in this shock-metamorphosed diopside grain. Based on high-pressure and high-temperature experiments, it was determined that the diopside grain in the Suizhou meteorite experienced a P-T regime of 20-24 GPa and 1800 - > 2000 degrees C. The orthorhombic (Ca0.663Mg0.314)SiO3 perovskite found in the Suizhou L6 chondrite could be considered as the third lower-mantle silicate mineral.