A new parameterization of hydrous mantle melting

Abstract

[1] Modeling of melt formation and transport in all tectonic settings requires the inclusion of water, since water has large effects on mantle solidi as well as physical properties of liquids. To facilitate the inclusion of water in melting models this paper presents a new parameterization for melt fraction as a function of pressure, temperature, water content and modal cpx, based on knowledge gained from recent advances in the fields of thermodynamic modeling as well as experimental investigations of peridotite melting and hydrous equilibria. The parameterization is computationally efficient and can be modified easily as better experimental data become available. We compare it to other published parameterizations and test it in simple calculations of adiabatic decompression melting (mid-ocean ridge) and hydrous melting (subduction zone).

Continental flood basalts derived from the hydrous mantle transition zone

“…This model is mainly based on the strong spatial correlation of geochemical features with distance of eruptive lavas relative to the edge of the stagnant slab. This is based on water partitioning in the Earth's mantle 18 , behaviour of slab-triggered wet upwelling and upward percolation 23,40 , hydrous mantle melting 51 , the mantle wedge model 21 , and upwelling from the hydrated mantle transition zone 24 . rocks from the Siberia 9 and Karoo 7 LIPs show that crustal contamination cannot be the controlling factor. Detailed geochemical and isotopic analyses of basaltic rocks from the Siberia 9 , Karoo 7 and Central Atlantic 6 LIPs demonstrate that their generations involved water and possibly other fluid phases released from subducted slabs and that their source reservoirs were both isolated and hydrated over a considerable period of time.…”

“…Because the wet upwelling of mantle requires no excess temperature in this model, there will be no thermal anomaly to result in pre-volcanic eruption surface uplift 62 . Also, some parts of the subducted slab may undergo dehydration melting and release water when it penetrates the 660-km discontinuity into the lower mantle 19 , whereas other subducted slab fragments may be entrapped in wet upwellings and returned to the upper mantle 10,51 . The latter provides a variant of the model that also accounts for the involvement of deep subducted slabs in the generation of large-scale intracontinental magmatism.…”

“…The wet upwellings will fertilize the shallow mantle (highlighted by yellow colour in Fig. 6) and decrease its solidus temperature, resulting in large-scale partial melting 51 . The temporal-spatial distribution of the Chifeng CFBs may thus be controlled by variations in slab stagnation and its final penetration of the 660-km discontinuity into the lower mantle.…”

Patterns in Galápagos Magmatism Arising from the Upper Mantle Dynamics of Plume‐Ridge Interaction

“…The melting calculations are based on the parameterized solidus-pressure relations and rate change in extent of melting F with temperature T (above the solidus, ∂F/∂T) of Katz et al [2003]. The more refractory DC matrix is treated as peridotite with 100 ppm water (i.e., C sw0 = 100 ppm) and the more fusible EC veins are treated as hydrous peridotite with 500 ppm water (i.e., C sw0 = 500 ppm).…”

“…For simplicity, we assume the garnet stability field ends and the spinel field begins abruptly at a pressure of 30 GPa; therefore, the extent of depletion (F 1 ) at which this transition occurs depends on temperature. The extent of depletion at which clinopyroxene is exhausted F 2 is assumed to be pressuredependent [Katz et al 2003], and therefore the point of clinopyroxene-out depends on temperature and depth.…”