Chemical bonding and the incorporation of potassium into the Earth's core

Journal Article · Tue May 01 00:00:00 EDT 1990 · Geophysical Research Letters (American Geophysical Union); (USA)

DOI:https://doi.org/10.1029/GL017i006p00693· OSTI ID:6114850

Sherman, D M ^[1]

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1. Geological Survey, Denver, CO (USA)

It has been argued that most of the Earth's potassium was segregated into the outer core and that the radioactive decay of {sup 40}K provided the heat source for the geodynamo. This idea rests on the assumption that the affinity of potassium for sulfur or metallic iron is enhanced at high pressure. In this paper, the high pressure electronic structures of K in sulfide, iron sulfide and metallic iron coordination environments were determined from molecular orbital (SCF-X{alpha}-SW) calculations on (KS{sub 8}){sup 15{minus}}, (KS{sub 8}Fe{sub 6}){sup 3{minus}} and KFe{sub 14} clusters. It is shown that, even at high pressure, potassium cannot alloy with metallic iron. Although a high-pressure electronic transition may enhance the potassium-sulfur chemical bond, the electronic structure of the KS{sub 8}Fe{sub 6} cluster shows that this electronic transition cannot happen in an iron sulfide melt. Consequently, potassium will not have an enhanced affinity for sulfur in planetary interiors. If the lower mantle were more reducing, potassium might be excluded from the silicate phases by more strongly lithophile elements and segregated into a metal sulfide phase in the outer core (cf. the phase assemblages in enstatite chondrites). Given the oxidation state of the Earth, however, it is unlikely that significant quantities of potassium have been incorporated into the outer core. The Earth, like the moon and the eucrite parent body, is depleted in potassium. An alternative heat source (e.g., the radioactive decay of U and Th) must be invoked to explain the geodynamo.

• OSTI ID: 6114850
• Journal Information: Geophysical Research Letters (American Geophysical Union); (USA), Vol. 17:6; ISSN 0094-8276
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
58 GEOSCIENCES
IRON SULFIDES
ELECTRONIC STRUCTURE
POTASSIUM ALLOYS
POTASSIUM SULFIDES
DECAY
EARTH CORE
EARTH MANTLE
HEAT SOURCES
INTERMETALLIC COMPOUNDS
PHASE TRANSFORMATIONS
POTASSIUM 40
PRESSURE DEPENDENCE
PRESSURIZATION
THORIUM
URANIUM
ACTINIDES
ALKALI METAL COMPOUNDS
ALKALI METAL ISOTOPES
ALLOYS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
CHALCOGENIDES
ELECTRON CAPTURE RADIOISOTOPES
ELEMENTS
IRON COMPOUNDS
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LIGHT NUCLEI
METALS
NUCLEI
ODD-ODD NUCLEI
POTASSIUM COMPOUNDS
POTASSIUM ISOTOPES
RADIOISOTOPES
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
YEARS LIVIN
360602* - Other Materials- Structure & Phase Studies
580000 - Geosciences