The Midcontinent Rift System (MRS) or Keweenawan Rift is a long geological

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...

in the center of the North American continent and south-central part of the North American plate. It formed when the continent's core, the

North American craton North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north'' ...

, began to split apart during the

Mesoproterozoic The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic ...

era of the

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

, about 1.1 billion years ago. The rift failed, leaving behind thick layers of

igneous rock Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

that are exposed in its northern reaches, but buried beneath later sedimentary formations along most of its western and eastern arms. Those arms meet at

Lake Superior Lake Superior is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. Lake Michigan–Huron has a larger combined surface area than Superior, but is normally considered tw ...

, which is contained within the

rift valley A rift valley is a linear shaped lowland between several highlands or mountain ranges produced by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear ...

. The lake's north shore in

Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...

and

Minnesota Minnesota ( ) is a U.S. state, state in the Upper Midwestern region of the United States. It is bordered by the Canadian provinces of Manitoba and Ontario to the north and east and by the U.S. states of Wisconsin to the east, Iowa to the so ...

defines the northern arc of the rift. From the lake, the rift's eastern arm trends south to central lower

Michigan Michigan ( ) is a peninsular U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest, Upper Midwestern United States. It shares water and land boundaries with Minnesota to the northwest, Wisconsin to the west, ...

, and possibly into

Indiana Indiana ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Michigan to the northwest, Michigan to the north and northeast, Ohio to the east, the Ohio River and Kentucky to the s ...

Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...

Kentucky Kentucky (, ), officially the Commonwealth of Kentucky, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Illinois, Indiana, and Ohio to the north, West Virginia to the ...

Tennessee Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...

, and

Alabama Alabama ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South, Deep Southern regions of the United States. It borders Tennessee to the north, Georgia (U.S. state), Georgia to the east, Florida and the Gu ...

. The western arm runs from Lake Superior southwest through portions of

Wisconsin Wisconsin ( ) is a U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest of the United States. It borders Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michig ...

Iowa Iowa ( ) is a U.S. state, state in the upper Midwestern United States, Midwestern region of the United States. It borders the Mississippi River to the east and the Missouri River and Big Sioux River to the west; Wisconsin to the northeast, Ill ...

, and

Nebraska Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...

to northeastern

Kansas Kansas ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the west. Kansas is named a ...

, and possibly into

Oklahoma Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...

Formation and failure

The rock formations created by the rift included

gabbro Gabbro ( ) is a phaneritic (coarse-grained and magnesium- and iron-rich), mafic intrusive igneous rock formed from the slow cooling magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...

and

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

intrusive rock Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form ''Igneous intrusion, intrusions'', such as batholiths, dike (geology), dikes, Sill (geology), sills, laccoliths, and volcanic necks.I ...

s and

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

s. In the Lake Superior region, the upwelling of this molten rock may have been the result of a hotspot which produced a triple junction.(Powerpoint presentation) The hotspot domed the rocks of the Lake Superior area. Voluminous basaltic lava flows erupted from the central axis of the rift, similar to the present-day rifting underway in the Afar Depression of the

East African Rift The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. It was formerly considered to be part of a l ...

system. The southwest and southeast extensions represent two arms of the triple junction while a third failed arm extends north into Ontario as the Nipigon Embayment. This failed arm includes

Lake Nipigon Lake Nipigon ( ; ; ) is a freshwater lake in Northwestern Ontario. Part of the Great Lakes drainage basin, it drains through the Nipigon River into Lake Superior. It is the largest lake entirely within the Canadian province of Ontario. Ety ...

, Ontario. The rift system may have been the result of extensional forces behind the continental collision of the

Grenville Orogeny The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, ...

to the east which in part overlaps the timing of the rift development. Later compressive forces from the Grenville Orogeny likely played a major role in the rift's failure and closure. Had the rifting process continued, the eventual result would have been sundering of the North American

craton A craton ( , , or ; from "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and rifting of contine ...

and creation of a sea. The Midcontinent Rift appears to have progressed almost to the point where the ocean intruded. But after about 15–22 million years the rift failed. (Abstract) The Midcontinent Rift is the deepest closed or healed rift yet discovered; no known deeper rift ever failed to become an ocean.

The rift today

Lake Superior occupies a basin created by the rift. Near the present lake, rocks produced by the rift can be seen on the surface of

Isle Royale Isle Royale (, ) is an Islands of the Great Lakes, island of the Great Lakes located in the northwest of Lake Superior and part of the U.S. state of Michigan. The island and the 450 surrounding smaller islands and waters make up Isle Royale Na ...

and the

Keweenaw Peninsula The Keweenaw Peninsula (, ) is a peninsula of the U.S. state of Michigan. Part of the greater landmass of the Upper Peninsula of Michigan, Upper Peninsula, the Keweenaw Peninsula projects about northeasterly into Lake Superior, forming Keweena ...

of the Upper Peninsula of Michigan, northwest Wisconsin, and on the North Shore of Superior in Minnesota and Ontario. Similar rocks are exposed as far south as

Interstate Park Interstate Park comprises two adjacent state parks on the Minnesota–Wisconsin border, both named Interstate State Park. They straddle ''the Dalles'' of the St. Croix River (Wisconsin-Minnesota), St. Croix River, a deep basalt gorge with gian ...

near

Saint Paul, Minnesota Saint Paul (often abbreviated St. Paul) is the List of capitals in the United States, capital city of the U.S. state of Minnesota and the county seat of Ramsey County, Minnesota, Ramsey County. As of the 2020 United States census, 2020 census, ...

, but elsewhere the rift is buried beneath more recent sedimentary rocks up to thick. Where buried, the rift has been mapped by gravity anomalies (its dense

ic rock increases gravity locally),

aeromagnetic survey An aeromagnetic survey is a common type of geophysical survey carried out using a magnetometer aboard or towed behind an aircraft. The principle is similar to a magnetic survey carried out with a hand-held magnetometer, but allows much larger are ...

s, and

seismic Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...

data. A slightly older but possibly related geologic feature is the Mackenzie Large Igneous Province in Canada, which extends from the

Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

Nunavut Nunavut is the largest and northernmost Provinces and territories of Canada#Territories, territory of Canada. It was separated officially from the Northwest Territories on April 1, 1999, via the ''Nunavut Act'' and the Nunavut Land Claims Agr ...

to near the

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, H ...

Northwestern Ontario Northwestern Ontario is a secondary region of Northern Ontario in the Canadian province of Ontario which lies north and west of Lake Superior and west of Hudson Bay and James Bay. It includes most of subarctic Ontario. Its western boundary is the ...

Natural resources

The

Proterozoic The Proterozoic ( ) is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...

Nonesuch Shale formation in the Keweenawan Rift contains enough organic carbon (greater than 0.5%) to be considered a potential

source rock In petroleum geology, source rock is a sedimentary rock which has generated hydrocarbons or which has the potential to generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sedim ...

for petroleum. Oil identified as Precambrian has been found seeping out of the Nonesuch Shale in the White Pine mine in Michigan. A few deep wells were drilled to explore for oil and gas in rift rocks as far southwest as Kansas. No oil and gas were found, but the explorations did make some deep rock samples available. These include two "dry holes" drilled by

Amoco Amoco ( ) is a brand of filling station, fuel stations operating in the United States and owned by British conglomerate BP since 1998. The Amoco Corporation was an American chemical and petroleum, oil company, founded by Standard Oil Company i ...

: a well in Alger County, Michigan in 1987 and 1988, and one in

Bayfield County, Wisconsin Bayfield County is a county located in the U.S. state of Wisconsin. As of the 2020 census, its population is 16,220. Its county seat is Washburn. The county was created in 1845 and organized in 1850. The Red Cliff Band of Lake Superior Chip ...

to a depth of in 1992. In 1987

also drilled a dry hole that penetrated rift sediments in Iowa. The Michigan Copper Country in the

Upper Peninsula The Upper Peninsula of Michigan—also known as Upper Michigan or colloquially the U.P. or Yoop—is the northern and more elevated of the two major landmasses that make up the U.S. state of Michigan; it is separated from the Lower Peninsula b ...

and

contains major

native copper Native copper is an uncombined form of copper that occurs as a natural mineral. Copper is one of the few metallic elements to occur in native form, although it most commonly occurs in oxidized states and mixed with other elements. Native coppe ...

deposits in Keweenawan-age rocks associated with the rift. A copper mining industry was developed in Precolumbian times, reactivated in the 1840s and continued for more than a century. Some low-grade copper and nickel deposits, among the largest in the world, also exist in the Duluth Complex north of the lake. Once thought to be uneconomic to mine, these deposits have attracted renewed interest from resource companies.

White hydrogen

White hydrogen could be found or produced in the Mid-continental Rift System at scale for a renewable

hydrogen economy The hydrogen economy is an umbrella term for the roles hydrogen can play alongside low-carbon electricity to reduce emissions of greenhouse gases. The aim is to reduce emissions where cheaper and more energy-efficient clean solutions are not ava ...

. Water could be pumped down to hot iron-rich rock to produce hydrogen and the hydrogen could be extracted.

Gallery

File:NA basement rocks.gif, Geological map of North America showing the Midcontinent Rift in white, here labeled Keweenawan Rift. Lake Superior now occupies the apex of the rift; the section to its north marked "SUPERIOR" is the

Superior Craton The Superior Craton is a stable fault block, crustal block covering Quebec, Ontario, and southeast Manitoba in Canada, and northern Minnesota in the United States. It is the biggest craton among those formed during the Archean period. A craton is a ...

File:Sleeping Giant PP.JPG, Sleeping Giant in

File:Isle Royale aerial.jpg, Eroded volcanic strata at

Image:Mount McKay Thunder Bay.jpg, A mafic sill at

Thunder Bay Thunder Bay is a city in and the seat of Thunder Bay District, Ontario, Canada. It is the most populous municipality in Northwestern Ontario and the second most populous (after Greater Sudbury) municipality in Northern Ontario. Its population i ...

, Ontario File:Palisade, Shovel Point.jpg, Cliffs at Palisade Head and Shovel Point in

File:JayCookeStatePark1.jpg, Saint Louis River in Jay Cooke State Park in Minnesota File:InterstateStateParkMN arf3.JPG, Dalles of the St. Croix River at Interstate State Park, Minnesota-Wisconsin

References

External links

"Mineral Deposits of the Midcontinent Rift System"
United States Geological Survey Mineral Resources Program, Eastern Mineral and Environmental Resources Science Center. A detailed and well-illustrated resource focusing on the mineral resources of the Midcontinent Rift and its geologic history. * Stein, Seth et al. (2016
"New Insights into North America’s Midcontinent Rift"
''

Eos In ancient Greek mythology and Ancient Greek religion, religion, Eos (; Ionic Greek, Ionic and Homeric Greek ''Ēṓs'', Attic Greek, Attic ''Héōs'', "dawn", or ; Aeolic Greek, Aeolic ''Aúōs'', Doric Greek, Doric ''Āṓs'') is the go ...

'', 97, https://doi.org/10.1029/2016EO056659. {{Use dmy dates, date=August 2019 Aulacogens Geologic provinces of the United States Geology of Alabama Geology of Indiana Geology of Iowa Geology of Kansas Geology of Kentucky Geology of Michigan Geology of Minnesota Geology of Nebraska Geology of Ohio Geology of Oklahoma Geology of Ontario Geology of Tennessee Geology of Wisconsin Mesoproterozoic rifts and grabens Large igneous provinces