The Penokean orogeny was a mountain-building episode that occurred in the early

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided i ...

about 1.86 to 1.83 billion years ago, in the area of

Lake Superior Lake Superior in central North America is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. and the third-largest by volume, holding 10% of the world's surface fresh wa ...

, North America. The core of this orogeny, the Churchill Craton, is composed of terranes derived from the 1.86–1.81 Ga collision between the

Superior Superior may refer to: *Superior (hierarchy), something which is higher in a hierarchical structure of any kind Places *Superior (proposed U.S. state), an unsuccessful proposal for the Upper Peninsula of Michigan to form a separate state *Lake ...

and

North Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe a ...

craton A craton (, , or ; from grc-gre, κράτος "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 ...

s. The orogeny resulted in the formation of the

Nena Gabriele Susanne Kerner (born 24 March 1960), better known as Nena, is a German singer and songwriter who rose to international fame in 1983 as the lead vocalist of the band Nena (band), Nena with the Neue Deutsche Welle song "99 Luftballons". I ...

and Arctica continents, which later merged with other continents to form the

Columbia Columbia may refer to: * Columbia (personification), the historical female national personification of the United States, and a poetic name for America Places North America Natural features * Columbia Plateau, a geologic and geographic region i ...

supercontinent. The name was first proposed by in reference to what is known as the Penokee Range, sometimes incorrectly called the

Gogebic Range The Gogebic Range is an elongated area of iron ore deposits located within a range of hills in northern Michigan and Wisconsin just south of Lake Superior. It extends from Lake Namakagon in Wisconsin eastward to Lake Gogebic in Michigan, or alm ...

, in northern

Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and t ...

and

Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...

. The Paleoproterozoic Penokean orogeny developed in an embayment on the southern margin of the Superior Craton. It extends east from Minnesota to the Grenville orogen near

Lake Huron Lake Huron ( ) is one of the five Great Lakes of North America. Hydrologically, it comprises the easterly portion of Lake Michigan–Huron, having the same surface elevation as Lake Michigan, to which it is connected by the , Straits of Mack ...

and south to the Central Plain in Wisconsin. It is composed of two domains separated by the Niagara Fault Zone: the southern, internal domain, the Wisconsin Magmatic Terranes, consists of Paleoproterzoic

tholeiitic The tholeiitic magma series is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma ...

and

calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic m ...

island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alon ...

rocks and calc-alkaline plutonic rocks; the northern, external domain consists of a

continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...

foreland basin A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithosphere ...

overlying an Archaean basement and includes the supracrustal rocks of the Animikie Group and Marquette Range Supergroup. The collision between the two domains around 1.88–1.85 Ga resulted in northward-directed thrusting and folding of the northern domain. Before this episode the area was a

passive continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...

occupied by a shallow sea, which created large

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

deposits including the

banded iron formation Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness ...

s of the

Iron Range The term Iron Range refers collectively or individually to a number of elongated iron-ore mining districts around Lake Superior in the United States and Canada. Much of the ore-bearing region lies alongside the range of granite hills formed by ...

s. The

orogeny Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An '' orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted ...

happened in two phases. First an

called the Pembine-Wausau terrane collided with the ancient North American craton along with volcanoes formed in its

back-arc basin A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most o ...

. The second phase involved a

microcontinent Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Caus ...

called the Marshfield terrane, which today forms parts of Wisconsin and Minnesota. The episode lasted about 10 million years. Hundreds of millions of years later, the Keweenawan Rift occurred in the same area creating the basin that would eventually become

. The remains of this

can be seen today as the Iron Ranges of Minnesota and Ontario, the Northern Highlands of Wisconsin and the

Upper Peninsula of Michigan The Upper Peninsula of Michigan – also known as Upper Michigan or colloquially the U.P. – 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 by ...

References

; Notes ; Sources * * * Orogenies of North America Paleoproterozoic orogenies Proterozoic North America Precambrian United States Geology of Michigan Geology of Minnesota Geology of Ontario Geology of Wisconsin {{tectonics-stub

See also

References