Tectonomagmatic Evolution of the Tectonomagmatic Evolution of the Midcontinent RiftMidcontinent Rift

North America (Laurentia)at 1.1 Ga

Continental Continental Rifting-Rifting- The creation of ocean basins

Mantle Plumes and

Flood Basalts

Magmatic Underplating of the Crust

A Consequence of Mantle Plume Magmatism

LIPs-Large Igneous Provinces

Simple Tectonic Model for the

MCR

Evidence of a Starting Mantle Plume

• Rapid early rates of volcanism

• Large total volume of mafic magmatism (> 20 km volcanic edifice in central axis of rift)

• εNd of mafic rocks = 0 to slightly +

North Shore

Volcanic

Gp Portage Lake volcanics

Powdermill Group

Mamainse Pt Volcanics

Osler Group

Chengwatana volcanics

Duluth Complex

Beaver Bay Complex

NipigonSills

LoganSills

Coldwell Complex

Mellen Complex

Michipichoten Island Volcanics

Isle Royale Fault

Douglas Fault

Main IgneousMain IgneousUnits of the Units of the MCRMCR

Geophysical Evidence of Underplating

Lo-PHi-P

Primitive Ol Tholeiite

DifferentiatedDifferentiatedBasalts of the NSVGBasalts of the NSVG

Geochronology of the MCR

Hoaglund (2010)

Proposed Tectonomagmatic Model for the Midcontinent Rift

Why Didn’t the MCREvolve to an Ocean Basin?- Dissipation of the Plume- Resurgence of Grenville Compression