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Limiting depth of magnetization in cratonic lithosphere
Author(s) -
Toft Paul B.,
Haggerty Stephen E.
Publication year - 1988
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl015i005p00530
Subject(s) - granulite , geology , craton , geochemistry , lithosphere , precambrian , magnetite , kimberlite , thermomagnetic convection , natural remanent magnetization , magnetization , rock magnetism , geophysics , petrology , remanence , facies , magnetic field , geomorphology , tectonics , mantle (geology) , seismology , physics , quantum mechanics , paleontology , structural basin
Values of magnetic susceptibility and natural remanent magnetization (NRM) of clinopyroxene‐garnet‐plagioclase granulite facies lower crustal xenoliths from a kimberlite in west Africa are correlated to bulk geochemistry and specific gravity. Thermomagnetic and AF demagnetization analyses identify magnetite (Mt) and native iron (Fe) as the dominant magnetic phases (totalling ≤0.1 vol.% of the rocks) along with subsidiary sulfides. Oxidation states of the granulites are ≤MW, observed Mt occurs as rims on coarse (∼1 µm) Fe particles, and inferred SD‐PSD Mt may be a result of oxidation of fine‐grained Fe. The deepest limit of lithospheric ferromagnetism is 95 km, but a limit of 70 km is most reasonable for the West African Craton and for modelling Magsat anomalies over exposed Precambrian shields.