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Observational constraints on mantle melt transport

Presented by: 
John MacLennan University of Cambridge
Date: 
Monday 15th February 2016 - 14:30 to 15:30
Venue: 
INI Seminar Room 1
Abstract: 
The review paper of Kelemen et al. (1997) summarised the key observations used to develop a model of rapid melt extraction in porous channels. Many subsequent observations have been acquired with the aim of refining estimates of the timescales of melt extraction from the mantle. Nevertheless, substantial uncertainty remains concerning how these observations can be used to characterise variation in melt transport velocities under basaltic volcanoes at spreading ridges and ocean islands. Uranium series disequilibria indicate that melt transport rates are almost certainly >1 m yr-1 and probably >50 m yr-1. An alternative method for estimating melt transport rates is based upon the observational record of the response of magmatism to loading and unloading of a mantle melting region. Such loading cycles may be generated by with glaciation and sea-level change. It is well-established that the record of volcanic productivity in certain regions of Iceland is strongly influenced by variations in the load from glaciation of the island. The minimal time-lag between deglaciation and a burst in volcanic productivity indicates that melt transport is rapid (>50 m yr-1). More recent analyses of seafloor morphology and temporal variation in hydrothermal activity at submerged mid-ocean ridges have made a tentative link between sea-level fall during glacial growth and increased magmatic activity during glacial terminations. This link can only work if melt extraction rates are <5 m yr-1. Further modelling work is required to investigate this link and to establish if a single physical framework can be used to reconcile the observations from Iceland with those from the submerged mid-ocean ridges.

A number of models of melt extraction have been developed in order to understand the emergence of rapid channelized melt flow. One promising research direction is the study of the behaviour of mantle where fusible heterogeneities sit in a more refractory matrix.
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University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons