DIFFERENT TYPES OF CASIO<SUB>3</SUB> IN THE EARTH’S MANTLE AND ITS GEOCHEMICAL HETEROGENEITY: THE JUINA AREA IN BRAZIL AS AN EXAMPLE

CaSiO3 inclusions in diamonds from the Juina area in Brazil have low Fe (0.08–0.53 wt. % FeO) and Al (0–1.52 wt. % Al2O3) concentrations; they belong to the ultramafic association. Two different types exist among CaSiO3 grains. Type I has a normal REEn pattern, while type II has a sinusoidal REEn pattern. Type I CaSiO3 associates with high-Mg – high-Ni protogenetic ferropericlase, and type II associates with high-Fe – low-Ni syngenetic ferropericlase. Thus, type I CaSiO3 grains are protogenetic, formed, like high-Mg – high-Ni ferropericlase, in the upper part of the lower mantle as davemaoite (CaSi-perovskite), and type II CaSiO3 were formed in the transition zone as breyite. The enrichment of CaSiO3 in REE, particularly in LREE, corresponds to high values of their partition coefficient CaSiO3/melt and shows the Ca-SiO3’s origin from a mantle material under high pressures. The isotope characteristics of the studied CaSiO3 demonstrate strong geochemical heterogeneity in the inclusions. The 87Rb/86Sr ratios in type II CaSiO3 (0.127–3.23) are 3–4 orders higher than in type I (0.0008). Even within a single diamond, different CaSiO3 grains have 87Rb/86Sr ratios varying from 0.014 to 3.23. The same is true for U/Pb isotope systematics (e. g., 238U/206Pb varies in one sample in an order of magnitude from 0.031 to 0.312) and, to some extent, for Sm/Nd ratios. This implies the geo-chemical heterogeneity in Deep Earth on a very small scale.