On the origin of noble gases in mantle plumes.
The chemical differences between deep- and shallow-mantle sources of oceanic basalts provide evidence that several distinct components coexist within the Earth's mantle. Most of these components have been identified as recycled in origin. However, the noble-gas signature is still a matter of debate and questions the preservation of primitive regions in the convective mantle. We show that a model where the noble-gas signature observed in Hawaii and Iceland comes from a pristine homogeneous deep layer would imply a primitive (3)He content and (3)He/(22)Ne ratio that are very unlikely. On the contrary, mass balances show that the partly degassed peridotite of a marble-cake mantle can be the noble-gas end-member with an apparent 'primitive'-like composition. This component is mixed with recycled oceanic crust in different proportions in the plume sources and in the shallow mantle. A recycling model of the mantle, involving gravitational segregation of the oceanic crust at the bottom of the mantle, potentially satisfies trace-element as well as noble-gas constraints.
Coltice
Nicolas
N
Department of Geosciences, Guyot Hall, Princeton University, NJ 08544-1003, USA. ncoltice@princeton.edu
Ricard
Yanick
Y
D001128:Argon / Q000032:analysis / Q000737:chemistry; D003198:Computer Simulation; D018534:Earth, Planet; D019418:Evolution, Chemical; D019419:Evolution, Planetary; D005246:Feedback; D019015:Geologic Sediments / Q000032:analysis*; D005844:Geology / Q000379:methods; D006254:Hawaii; D006371:Helium / Q000032:analysis / Q000737:chemistry; D006358:Hot Temperature; D007055:Iceland; D007554:Isotopes / Q000032:analysis* / Q000737:chemistry; D008956:Models, Chemical; D008962:Models, Theoretical; D009356:Neon / Q000032:analysis / Q000737:chemistry; D005741:Noble Gases / Q000032:analysis* / Q000737:chemistry; D009792:Oceans and Seas; D018707:Volcanic Eruptions
D007554:Isotopes; D005741:Noble Gases; D006371:Helium; D009356:Neon; D001128:Argon