The Blake River Megacaldera Complex is a giant subaqueous

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

cluster or a nested caldera system that spans across the

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...

–

Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirte ...

border in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

. The caldera complex is around 2.7 billion years old, consisting of a series of overlapping

s of various ages and sizes. It lies within the southern zone of the Abitibi greenstone belt of the

Superior Craton The Superior Craton is a stable 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 larg ...

and has an area of . The Blake River Megacaldera Complex has been a centre of major interest since 2006 with numerous excursions at the international, national and local level.ASH FALL: Newsletter of the Volcanology and Igneous Petrology Division Geological Association of Canada
Retrieved on 2007-09-21 It is a world-class metallotect with respect to both hydrothermal Cu- Zn massive sulfides and

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile ...

-rich massive sulfides.

Structure and geographical extent

The Blake River Megacaldera Complex consists of mainly

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...

to intermediate volcanic flows and less abundant

felsic In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, wh ...

volcanic flows and intercalated

pyroclastic rock Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyrocl ...

s, which underwent three stages of major volcanic activity. * The first phase resulted in the creation of the long, wide, east-west striking Misema Caldera which has been dated to 2704–2707 Ma. It is a coalescence of at least two large mafic

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more vi ...

es that formed more than 2703 million years ago. * The second phase resulted in the creation of the long, wide, northwest–southeast trending

New Senator Caldera The New Senator Caldera is a large Archean caldera complex within the heart of the Blake River Megacaldera Complex, Quebec, Canada. It has a diameter of 15-30 kilometers and is made of thick massive mafic sequences. The caldera complex has in ...

which formed 2701–2704 Ma. Its formation consists of thick massive

sequences which has inferred to be a subaqueous

lava lake Lava lakes are large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression. The term is used to describe both lava lakes that are wholly or partly molten and those that are solidified (someti ...

during the early stages of the caldera's development. * The third phase of activity constructed the classic east-northeast striking 2696 Ma Noranda Caldera which contains a 7-to-9-km-thick succession of mafic and

rocks erupted during five major series of activity. The Blake River Megacaldera Complex is considered a

supervolcano A supervolcano is a volcano that has had an eruption with a Volcanic Explosivity Index (VEI) of 8, the largest recorded value on the index. This means the volume of deposits for such an eruption is greater than 1,000 cubic kilometers (240 cubi ...

due to its great size and its multiple dikes and vents. The Misema Caldera is in the order of , making the complex similar to the

Yellowstone Caldera The Yellowstone Caldera, sometimes referred to as the Yellowstone Supervolcano, is a volcanic caldera and supervolcano in Yellowstone National Park in the Western United States. The caldera and most of the park are located in the northwest corn ...

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to t ...

, Lake Toba in

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...

and strikingly similar in structure to the

Olympus Mons Olympus Mons (; Latin for Mount Olympus) is a large shield volcano on Mars. The volcano has a height of over 21.9 km (13.6 mi or 72,000 ft) as measured by the Mars Orbiter Laser Altimeter (MOLA). Olympus Mons is about two and a ha ...

caldera on

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

. As a result, the Blake River Group is best categorized as a meganested caldera complex.Blake River Group evolution: characteristics of the subaqueous Misema and New Senator calderas
Retrieved on 2008-01-23

References

{{Clear Calderas of Ontario Calderas of Quebec Supervolcanoes Volcanic groups Archean calderas Polygenetic volcanoes Landforms of Abitibi-Témiscamingue

Structure and geographical extent

See also

References