Joyce Shi Sim

Large scale organization of melt focusing beneath mid-ocean ridges using new open-sourced two phase M3LT models

Author: Joyce Shi Sim

Magmatism at mid-ocean ridges generates new oceanic crust and accounts for 90% of global volcanism. The oceanic crust is emplaced in a narrow neo-volcanic region (e.g. Macdonald (1982); Carbotte et al. (2016)), whereas basaltic melt is generated in a wide region beneath mid-ocean ridges as
suggested by a few geophysical surveys (Forsyth et al., 1998b; Key et al.,
2013). A number of focusing mechanisms have been proposed such as ridge
suction (Spiegelman and McKenzie, 1987) and decompaction layers (Sparks
and Parmentier, 1991). We present results from a suite of two-phase mod-
els applied to the mid-ocean ridges with varying half spreading rate using
a new open source model, M3LT, to explore the dynamics of Melt in the
Mantle beneath Mid-ocean ridges (Sim et al., 2018). M3LT is built using
TerraFERMA (Wilson et al., 2017). The amount of oceanic crust versus
half spreading rate generated by our models are within observations from
active seismic surveys (White et al., 1992; Bown and White, 1994; White
et al., 2001; Harding et al., 2017). Our models suggest that the suppres-
sion of porosity waves with increasing half spreading rates contributes to
the decrease of oceanic crustal thickness variations. There are three melt
focusing mechanisms present in our models, namely: ridge suction from in-
compressible shear, decompaction layers and the recently discovered melting
rate focusing. Further analyses suggest that melting rate focusing decreases
slightly with spreading rate whereas melt focusing from decompaction lay-
ers increase rapidly below half spreading rate of 4 cm/yr and then decrease
slightly for half spreading rate more than 4 cm/yr. Melting rate focusing is
persistent regardless of spreading rates and it focuses a higher proportion of melt produced at slower spreading rates.