On the degassing state and the chemical structure of the Earth's interior inferred from noble gas isotopes-Past and recent views

Abstract

The degassing state of the Earth's interior is one of the main issues in relation to the evolution of the Earth and has been discussed by many investigators over several decades. I outline some trials to reveal the state of degassing based on noble gas isotopes. Then, based on noble gas isotope signatures so far obtained, I discuss models of the chemical structure of the Earth's interior which are inevitably related to the degassing state of the Earth. I propose a preferred model which suggests the possibility for the occurrence of relatively undegassed and possibly less fractionated reservoir(s) in the Earth's deep interior, which might be located in a relatively non-convective mantle.

Conjecture with water and rheological control for subducting slab in the mantle transition zone

“…However, the once trapped crustal materials sink into the lower mantle within 20e30 Myr from the start of the plate subduction, a relatively short time as compared with the whole mantle convection cycle (up to w200 Myr). The results of this study suggest recycling of crustal material in the whole mantle, which is consistent with the evidence from mantle geochemistry (e.g., Albarède, 1998;Coltice and Ricard, 1999) as opposed to two-layer mantle convection models (e.g., O'Nions and Oxburgh, 1983;Allègre et al, 1986;Allègre, 1987) (see reviews by Kaneoka, 1995Kaneoka, , 2008Hofmann, 1997;Tackley, 2000Tackley, , 2007.…”

Imaging paleoslabs in the D″ layer beneath Central America and the Caribbean using seismic waveform inversion

“…We note that if the convection in the lower mantle is isolated from the convection in the upper mantle ( 46 ), the high-velocity anomalies “CA” and “VZ” ( Fig. 4 ) that we observe at the CMB might be colder-than-average material related to downflow in the isolated lower mantle.…”