(ORDO NEWS) — A team of scientists led by geologist Byeongkwan Ko from the University of Michigan has revealed that in the depths of the Earth, at a depth of 2,900 kilometers, there are conditions for the formation of a previously unknown mineral substance.
Extremely high pressures and temperatures contribute to the formation of calcium-rich bridgmanite, which is changing the way we look at the mineralogy of the lower mantle, according to a study published in the journal Nature.
It is believed that the lower mantle of the Earth consists of three main mineral phases: ferropericlase (Mg,Fe)O and two perovskites – bridgmanite (Mg,Fe)(Al,Si)O3 and davemaoite (CaTiO3).
Perovskites are mineral structures with the formula ABX3 that are known to have unusual properties, including superconductivity. At great depths, under conditions of high temperature, minerals with a similar crystal structure merge, forming new minerals.
Although it has been shown that davemaoite is absent in environments with high temperatures and pressures typical of the lower mantle, it cannot be completely dissolved in bridgmanite containing magnesium and silicon.
Scientists suspected that, under specific conditions, davemaoite could completely merge with bridgmanite to form a single perovskite phase in the lower mantle.
Many attempts have been made to find these conditions, but the results of the experiments always gave two perovskite phases. In the new work, the scientists investigated the solubility of CaTiO3 in bridgmanite containing iron and aluminum.
The temperature of the samples was sharply raised to 1800-3000 kelvins at a pressure of 33-110 gigapascals.
For this purpose, cells with diamond anvils and laser heating were used, and the transformations of minerals were monitored by X-ray diffraction at the Advanced Photon Source synchrotron radiation source at the Argonne National Laboratory.
It has been shown that the solubility of calcium in bridgmanite increases dramatically at a temperature of about 2300 Kelvin and above 40 GPa to a level sufficient to completely dissolve all CaSiO3.
This leads to the disappearance of perovskite CaSiO3 at depths greater than 1800 kilometers and the appearance of calcium-enriched bridgmanite. Iron plays a key role in this process in bridgmanite, increasing the solubility of calcium.
Thus, a deeper lower mantle with a sufficiently high temperature should have a different mineralogical composition than a shallower lower mantle.
Since the interior of the early Earth was much warmer, most of the lower mantle contained a single perovskite phase and its mineralogy was significantly different from today’s.
However, it is not yet known whether this could have affected important global processes such as plate tectonics or the Great Oxygen Event 2.45 billion years ago.
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