Abstract
Abstract. The most profound consequences of the presence of Ca–Mg carbonates
(CaCO3–MgCO3) in the Earth's upper mantle may be to lower the
melting temperatures of the mantle and control the melt composition.
Low-degree partial melting of a carbonate-bearing mantle produces
CO2-rich, silica-poor melts compositionally imposed by the
melting relations of carbonates. Thus, understanding the melting relations
in the CaCO3–MgCO3 system facilitates the interpretation of
natural carbonate-bearing silicate systems. We report the melting relations of the CaCO3–MgCO3 system and
the partition coefficient of trace elements between carbonates and carbonate
melt from experiments at high pressure (6 and 9 GPa) and temperature
(1300–1800 ∘C) using a rocking multi-anvil press. In the
absence of water, Ca–Mg carbonates are stable along geothermal
gradients typical of subducting slabs. Ca–Mg carbonates
(∼ Mg0.1–0.9Ca0.9–0.1CO3) partially melt
beneath mid-ocean ridges and in plume settings. Ca–Mg carbonates
melt incongruently, forming periclase crystals and carbonate melt between 4
and 9 GPa. Furthermore, we show that the rare earth element (REE) signature
of Group-I kimberlites, namely strong REE fractionation and depletion of
heavy REE relative to the primitive mantle, is resembled by carbonate
melt in equilibrium with Ca-bearing magnesite and periclase at 6 and
9 GPa. This suggests that the dolomite–magnesite join of the
CaCO3–MgCO3 system might be useful to approximate the REE
signature of carbonate-rich melts parental to kimberlites.
Funder
Deutsche Forschungsgemeinschaft
Subject
Pulmonary and Respiratory Medicine,Pediatrics, Perinatology and Child Health
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