Arctic Field Projects



Project Title: Measuring mantle hydrogen content to map ore-forming fluids and model plate tectonics (Award# FT150100541)

PI: Selway, Katherine (Kate) Mary (kate.selway@mq.edu.au)
Phone: 61(2) 9850 7992 
Institute/Department: Macquarie University, Department of Earth and Planetary Sciences 
IPY Project?
Funding Agency: AU\Research/Higher Ed
Program Manager: Dr. Jennifer Mercer (jmercer@nsf.gov)
Discipline(s): | Geological Sciences\Geophysics | Geological Sciences\Glaciology |

Project Web Site(s):
Project: https://summatgreenland.wordpress.com/

Science Summary:
This project uses the geophysical method magnetotellurics (MT), which images the electrical conductivity of the Earth to depths of ~400 km. In Greenland, the aim of this work is to constrain mantle viscosity and improve ice-loss calculations. The electrical conductivity of the Earth’s upper mantle is most strongly controlled by temperature, hydrogen content and the presence of melt. These three factors also control its viscosity (resistance to flow), so MT data are one of the best ways to measure mantle viscosity. This is particularly important for Greenland since viscosity is one of the most important and poorly constrained inputs into glacial isostatic adjustments models. These models seek to account for the mantle’s slow response to past changes in ice sheet thickness and to remove this long-term signal from current measurements of ice loss. Greenland’s mantle viscosity is likely to be particularly complex. Mantle rocks from northern and southern Greenland are ancient, with cold temperatures and depleted compositions that would be expected to have high viscosity. However, the Iceland Plume passed beneath central Greenland ~40 to 100 million years ago, and that section of mantle is likely to have been heated and hydrated, giving it a lower viscosity. This project’s long-term aim is to collect MT data over several areas on Greenland to image the mantle both over the Iceland Plume track and distal from it. Summit Station is ideally located to image the Greenland mantle that has been impacted by the Iceland Plume. They will model the data and interpret the results in terms of mantle viscosity and then feed these viscosity calculations into improved glacial isostatic adjustment models. The MT data will also image any sub-ice melt layers, so they will also be able to test the hypothesis that increased surface heat flow over the Iceland Plume track is leading to increased sub-ice melting. In the work at Summit in 2018, researchers plan to carry out an initial study in which they will: (1) Deploy two long-period instruments in the vicinity of Summit to provide information on mantle conductivity, electrical dimensionality and strike direction, in order to plan the geometry of future, deep-field campaigns. (2) Deploy a network of broad-band instruments in the vicinity of Summit to investigate the presence of basal melt layers. (1) Test different instruments and electrodes in side-by-side tests to compare data quality and determine optimal instrument configurations. MT instruments are passive (only recording naturally occurring electric and magnetic fields) and are powered by batteries and solar panels. They consist of a magnetometer or magnetometers, which must be shallowly buried for stability, a logger unit, and two electric dipoles, which consist of metal plates shallowly buried in snow/ice, separated by ~100 m. The whole area for a station deployment is therefore ~100 x 100 m. The sensors are extremely sensitive so stations must be deployed at least ~1 km from electrical noise and physical vibrations.

Logistics Summary:
This is an Australian-funded pilot project to visit Summit Station, Greenland. The project will use the geophysical method magnetotellurics (MT), which images the electrical conductivity of the Earth to depths of ~400 km. Summit Station is ideally located to image the Greenland mantle that has been impacted by the Iceland Plume. Station installation takes two to four hours. Broad-band stations have a recording time of approximately one day, whereas for the long-period stations a recording time of two to three weeks allows good resolution of mantle depths. For the long-period stations, researchers would request that a Summit technician, who they would train, bring in the stations after they have left so that the researchers do not need to stay longer than necessary. Stations will be deployed within the Summit permit zone and specific locations will be planned to avoid any sensitive areas. In July of 2018 researchers will travel to Summit Station, via the Air National Guard (ANG) from Kangerlussuaq, to conduct an initial study in which they will deploy two long-period instruments and a network of broad-band instruments near Summit to investigate the presence of basal melt layers. They will travel to the work sites via snowmachine on day trips.

CPS will provide Air National Guard (ANG) coordination for passengers and cargo, camping and communication equipment, snowmachine use, science technician support, and Summit Station user days. NSF will recoup the costs of CPS support directly from the sponsoring institute. The PI will pay for all other arrangements, including KISS user days, food in Kangerlussuaq, stateside freight and commercial travel, through the grant.
SeasonField SiteDate InDate Out#People
2018Greenland - Kangerlussuaq07 / 13 / 2018 07 / 26 / 20184
2018Greenland - Summit07 / 15 / 2018 07 / 22 / 20184
 


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