G013-02
How magnetotellurics can aid cryosphere studies: mantle rheology, GIA, surface heat flow and basal melting.
Monday, 14 December 2020: 05:34
Virtual
Kate Selway1, Clinton P Conrad2, Florence Ramirez3,4, Nanna B. Karlsson5, Maaike Weerdesteijn4 and Björn Heyn4, (1)Macquarie University, Sydney, NSW, Australia, (2)University of Oslo, Centre for Earth Evolution and Dynamics, Oslo, Norway, (3)Macquarie University, Sydney, Australia, (4)University of Oslo, Centre for Earth Evolution and Dynamics (CEED), Oslo, Norway, (5)Geological Survey of Denmark and Greenland, København K, Denmark
Abstract:
Magnetotelluric (MT) models are an under-utilized resource in studies of the cryosphere. Both seismic and magnetotelluric (MT) data can image the Earth’s upper mantle and provide important constraints on mantle rheology for glacial isostatic adjustment (GIA) studies and on mantle geotherms for surface heat flow studies. While seismic models have historically been utilised for these cryosphere studies, MT models have not yet been used so extensively. MT images the electrical conductivity of the Earth and is a useful tool for constraining rheology because the dominant factors that control mantle conductivity – temperature, the presence of partial melt, and the hydrogen content of mantle minerals – also control mantle rheology. While seismic data are sensitive to temperature and partial melt they are not sensitive to hydrogen content, so the incorporation of MT data in GIA studies can produce more accurate results than using seismic data alone. Since both seismic and MT data are sensitive to temperature, a combined analysis can also produce improved constraints on surface heat flow. In addition, MT can image basal melt-water beneath thick ice sheets and can therefore help to investigate links between surface heat flow and basal melting.
As well as a description of the application of MT to studies of the cryosphere, this talk will include recent results from Svalbard and Greenland that illustrate how MT can improve models of mantle rheology for GIA. In Svalbard, uncertainties in ice sheet history models have led to large uncertainties in mantle rheology from GIA, and a complex tectonic setting has led to ambiguity between different seismic models. Using new MT data, we have imaged a layer of partial melt in the shallow mantle and developed new upper mantle viscosity profiles that can help to constrain the ice sheet history. In Greenland, we have collected the first ever MT data on the Greenland Ice Sheet. This work aims to measure 3D mantle viscosity variations beneath Greenland as well as targetted imaging of basal melt and is being combined with the development of an open-source GIA code that includes 3D viscosity variations.
