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Helium isotope variations in Juan De Fuca Ridge basalts
Author(s) -
Lupton John E.,
Graham David W.,
Delaney John R.,
Johnson H. Paul
Publication year - 1993
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 - 10.1029/93gl01271
Subject(s) - seamount , basalt , geology , mantle (geology) , hotspot (geology) , isotopes of helium , mid atlantic ridge , helium , geochemistry , ridge , mineralogy , paleontology , seismology , physics , atomic physics
We have measured ³He/ 4 He ratios and He and Ne concentrations on a suite of 24 basalt glasses from the neovolcanic zone of the Juan de Fuca Ridge (JdFR) from 44.6°N near the Blanco Transform up to 48.0°N on the Endeavour Segment. The helium isotope ratios exhibit a clear geographic variation, with relatively constant values of 7.8 R A along the southern JdFR increasing to a maximum of 8.8 R A at 46.9°N on the Cobb Segment, and then dropping to values of ∼8.0 R A at the Cobb Offset. Ratios along the Endeavour Segment further north are somewhat higher, averaging ∼8.2 R A . Basalts dredged from Axial Seamount have ³He/ 4 He = 7.9–8.4 R A , indicating that the seamount does not have a geochemical or isotopic signature distinct from other portions of the JdFR. This confirms that while Axial Seamount is the locus of excess magma generation, it is devoid of any hotspot or ocean island basalt geochemical signature. For the whole sample set, ³He/ 4 He ratios show a negative correlation with 87 Sr/ 86 Sr. We attribute the geographical variations in ³He/ 4 He to broad‐scale heterogeneity in the mantle source region beneath the JdFR. Beginning at Axial Seamount and further north, ³He/ 4 He shows a positive correlation with Fe 8.0 , suggesting that melting dynamics in the underlying mantle may exert some control on the helium isotope ratios along part of our survey area.