Ancient mantle plume trail beneath the North American Midcontinent Rift revealed from Magnetotelluric data

The Midcontinent Rift (MCR) system formed ~1.1 Ga is a failed continental rift within the Superior Province of the Archean Laurentian continent. It is one of the important Precambrian geological features in the North American midcontinent. The abundance of igneous rocks exposed in the vicinity of Lake Superior contemporaneous to MCR is thought to be related to the upwelling of a Keweenaw mantle plume or anomalously hot/enriched mantle. However, in contrast to the classic three-arm model of continental rifting above a mantle plume, the lack of a northward-trending third rift branch or aulacogen in the MCR and the ~300 km deviation of the main rift arms from the inferred center of the mantle plume have not yet been well explained. To investigate this unique mantle plume-rift relationship and better constrain the influence range of the Keweenaw mantle plume, this study builds a three-dimensional electrical resistivity crust-upper mantle model that extends northward from the MCR to the Archean Superior Province using magnetotelluric (MT) data from the United States EarthScope and Canadian Lithoprobe project. The model reveals a prominent high conductivity anomaly near the base of the Western Superior Craton's lithospheric mantle, which is northwest-southeast trending, crosses the western branch of the MCR, and extends more than 300 km to both sides. It is inferred that the anomaly reflects an ancient mantle plume trail and is caused by the metasomatism and/or partial melting of the sulfide-rich basal lithospheric mantle during the Keweenaw mantle plume impingement.