LITHOPROBE Slave-Northern Cordillera Lithosphere Evolution (SNORCLE) Transect
Slave Lakes EM Experiment

Constructing an instrument
Helmut and Bill construct a shallow-water EM instrument in preparation for deploying it in the middle of one of the lakes. In the background Rob is supervising.

EM leaders.....


Financial Sponsors.....

Project Overview.....

A better understanding of how the mantle participated in the growth and stabilization of ancient cratons is central to the study of the evolution of the continents. There are several current and competing models for the formation of Archean and Proterozoic cratons. However, these models are often in conflict, reflecting the limited extant data that can sense the deep structure beneath continents. A program of multi-disciplinary geoscientific studies of Archean cratonic roots is required to remedy fundamental deficiences in our knowledge base so that we can better address continental mantle issues.

Electromagnetic studies have demonstrated that they can contribute significantly to such studies by defining both the base of the lithosphere (as determined by the onset of partial melt in the asthenosphere, or approximately the locus of the present-day 1300 C isotherm) and by determining structural features (both in a lateral and a vertical sense) within the mantle. In addition, electromagnetic studies can define the fossil foliation and lineation direction from the strike of mantle electrical anisotropy. Thus, electromagnetic methods should serve as a key component of modern continental studies that complement and augment the information provided by seismic methods, particularly shear wave splitting studies.

This research is a major add-on component of a multi-disciplinary effort that is currently underway as part of the Canadian Lithoprobe program. We are proposing to utilize proven oceanic magnetotelluric technology in strategically-located lakes on the Archean Slave province to conduct very deep magnetotelluric probing of cratonic root structure. Lakes offer a thermally and chemically stable environment for long period electromagnetic measurements that cannot be matched on land. To be specific, we propose to characterize electrically the root of the southern and central portion of the Slave craton, including its depth extent, any lateral variation in structure, and its deep electrical anisotropy. We will combine our results with ongoing Canadian broadband magnetotelluric, reflection seismic, passive seismic (especially shear wave splitting), and related geological studies in an effort to improve our overall understanding of deep cratonic structure.

The choice of the Slave craton is determined by a number of factors, including:

We view this work as the first phase of a larger scale effort to electromagnetically characterize Archean cratonic mantle where co-located high quality passive seismic experiments have either taken place, are taking place, or are planned. Deep electromagnetic methods have not been applied as much as equivalent passive seismic ones, and accordingly we view this work as a pilot project, although the instrumentation, methods and analyses are all well-proven. Should this study be as successful as we expect, then later research will focus on other cratons, such as the Superior or Kaapvaal.

EM Activities.....

1998 installation
Slave geology and EM sites - JPG
Press for full-sized map
(178 Kb - JPG) or download CorelDraw CDR file (4.8 Mb) or a CMX file (2.4 Mb).
Shallow-water instruments were placed in 10 lakes on the Slave craton. The locations are shown by the red stars on the map. The lakes are:
Northern Line:
Point Lake, Contwoyto Lake, Rockinghorse Lake
Middle Line:
Indin Lake, Snare Lake, Big Lake, Lac de Gras
Southern Line:
Wheeler Lake, Duncan Lake, Lac Tet d'Ours

The lakes with the small red stars are those where the electric fields may go off-scale due to a software bug found after their installation.

Other sites are from the SNORCLE 1996 MT data acquisition (yellow circles) and the 1998 Winter Road experiment (black squares)

Pictures of construction, deployment and retireval

(JPEG format: 200Kb - 300Kb each)


MTNet Home Page Alan's Home Page

Alan G Jones / 22 April 2006 /