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the two‐faced mica
Author(s) -
York Derek,
Martinez Margarita Lopez
Publication year - 1986
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/gl013i009p00973
Subject(s) - biotite , mica , argon , geology , isotopes of argon , spectral line , mineralogy , astrophysics , physics , atomic physics , paleontology , astronomy , quartz
We explain two common 40 Ar/ 39 Ar age spectra shapes in biotite. One features a dip in ages at mid‐temperature regions of the spectrum. The other has exactly the opposite characteristic, i.e. a bump upwards in age at the same position. The explanation assumes that the vast majority of biotites consist of two almost completely independent K‐Ar phases. During laboratory step‐heating of irradiated biotite, the argon from these two phases is separated via release over two different temperature ranges. Biotite is therefore a clock with two faces.