Clues about lower mantle chemistry from natural samples of bridgmanite

English Abstract:

Bridgmanite, MgSiO₃ in an ABO₃ perovskite structure, was established in 2014 as a mineral by means of structural and chemical characterization of a natural specimen (ref 1). This natural specimen was identified in a shock melt vein in the Tenham L6 chondrite. By now we have identified bridgmanite in a martian meteorite also. I will show that natural samples of brigdmanite provide a useful complement to experimetal studies of this mineral: Bridgmanite in clasts trapped chondrite shock melt veins inherits the composition of precursor pyroxenes and, thus, samples an extended compositional range, quite beyond of what has been synthesized. This provides relevant information upon endmember compositions and volumes.

Bridgmanite in martian meteorites occurs in assemblies that crystallized from or in contact to melt. These assemblies provide insights in minor-element distribution between melt and lower mantle rock forming minerals. I compare these findings to experimental results and discuss the possible implications for incompatible element differentiation in the mantle.

Ref 1: Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite, O. Tschauner, C. Ma, J. Beckett, C. Prescher, V. Prakapenka,G.Rossman, Science 346, 110-1102, DOI: 10.1126/science.1259369 (2014)