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The 40 Ar/ 36 Ar ratio of the undepleted mantle; A reevaluation
Author(s) -
Matsuda Junichi,
Marty Bernard
Publication year - 1995
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 - 10.1029/95gl01893
Subject(s) - mantle (geology) , argon , basalt , geology , mixing ratio , mantle plume , analytical chemistry (journal) , physics , geophysics , atomic physics , chemistry , geochemistry , lithosphere , paleontology , atmospheric sciences , chromatography , tectonics
The 40 Ar/ 36 Ar ratio of the mantle bears important information about the extent of early degassing of the earth. Many researchers have agreed that 40 Ar/ 36 Ar ratio in the depleted mantle as sampled by Mid‐Ocean Ridge Basalts (MORB) is as high as 28000. However, the 40 Ar/ 36 Ar ratio in the undepleted mantle has been strongly debated. We have reexamined the noble gas data of He and Ar in MORB and hot spot volcanics using 4 He/ 40 Ar vs. 36 Ar/ 40 Ar and 4 He/ 40 Ar vs. ³He/ 40 Ar diagrams. In these diagrams, mixing lines between two components result in straight lines, which enable us to interpret data more easily than using diagrams with different denominators like a 40 Ar/ 36 Ar vs. ³He/ 4 He plot where all mixing lines appear as curves. We conclude that the 40 Ar/ 36 Ar ratio in the undepleted mantle is much higher than the atmospheric value and should be higher than the observed highest values in the hot spot volcanics. We also suggest that high 4 He/ 40 Ar ratios observed in MORB result from kinetic disequilibrium during partial melting.