Sturgeon Lake Caldera
Encyclopedia
Sturgeon Lake Caldera is a large extinct caldera
complex in Kenora District
of Northwestern Ontario
, Canada
. It is one the world's best preserved mineralized
Neoarchean
caldera complexes, containing well-preserved mafic
-intermediate pillow lava
s, pillow breccia
s, hyaloclastite
and peperite
s, submarine lava dome
s and dome-associated breccia deposits. The complex is some 2.7 billion years old with a minimum strike
length of 30 km (19 mi).
intrusive
, volcanic
, and sedimentary
layers. This piecemeal caldera complex includes nearly 3000 m (9,843 ft) of major subaqueously deposited intracaldera fill. Episodes of subaerial and subaqueous explosive felsic
volcanism created rhyodacitic
to rhyolitic
tuff
s and lapilli
tuffs. The caldera complex lies in the Wabigoon greenstone belt.
The Sturgeon Lake Caldera contains volcanic units that outcrop over 30 kilometers from east to west with up to five separate, major ash flow tuff units with thickness ranging from 100 m (328 ft) to 1200 m (3,937 ft). The Mattabi pyroclastic flow, with a thickness in excess of 800 m (2,625 ft) and a strike length of at least 30 km (19 mi), is the third and most voluminous eruptive event associated with the Sturgeon Lake Caldera. It hosts the 12-Mt Mattabi massive sulfide deposit
which is interpreted to have formed on and below the seafloor, the latter through the processes of pore-space filling and replacement.
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
complex in Kenora District
Kenora District, Ontario
Kenora District is a district and census division in Northwestern Ontario, Canada. It was created in 1907 from parts of Rainy River District. It is, geographically, the largest division in that province; at 407,192.66 km2 it comprises almost 38 percent of the province's land area...
of Northwestern Ontario
Northwestern Ontario
Northwestern Ontario is the region within 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 Canadian province of Manitoba, which disputed Ontario's claim to the...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. It is one the world's best preserved mineralized
Mineralization (geology)
In geology, mineralization is the hydrothermal deposition of economically important metals in the formation of ore bodies or "lodes".The first scientific studies of this process took place in Cornwall, United Kingdom by J.W.Henwood FRS and later by R.W...
Neoarchean
Neoarchean
The Neoarchean is a geologic era within the Archaean. It spans the period of time from —the period being defined chronometrically and not referenced to a specific level in a rock section on Earth...
caldera complexes, containing well-preserved mafic
Mafic
Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...
-intermediate pillow lava
Pillow lava
Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in...
s, pillow breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
s, hyaloclastite
Hyaloclastite
Hyaloclastite is a hydrated tuff-like breccia rich in black volcanic glass, formed during volcanic eruptions under water, under ice or where subaerial flows reach the sea or other bodies of water. It has the appearance of angular flat fragments sized between a millimeter to few centimeters...
and peperite
Peperite
A Peperite is a sedimentary rock that contains fragments of igneous material and is formed when magma comes into contact with wet sediments. The term was originally used to describe rocks from the Limagne region of France, from the similarity in appearance of the granules of dark basalt in the...
s, submarine lava dome
Lava dome
|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...
s and dome-associated breccia deposits. The complex is some 2.7 billion years old with a minimum strike
Strike and dip
Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented...
length of 30 km (19 mi).
Geology
The Sturgeon Lake Caldera contains a well preserved north facing homoclinal chain of greenschist facies metamorphosedMetamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
intrusive
Intrusion
An intrusion is liquid rock that forms under Earth's surface. Magma from under the surface is slowly pushed up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years. As the rock slowly...
, volcanic
Volcanic rock
Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it is an igneous rock of volcanic origin...
, and sedimentary
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
layers. This piecemeal caldera complex includes nearly 3000 m (9,843 ft) of major subaqueously deposited intracaldera fill. Episodes of subaerial and subaqueous explosive felsic
Felsite
Felsite is a very fine grained volcanic rock that may or may not contain larger crystals. Felsite is a field term for a light colored rock that typically requires petrographic examination or chemical analysis for more precise definition...
volcanism created rhyodacitic
Rhyodacite
Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of granodiorite. Phenocrysts of sodium rich plagioclase, sanidine, quartz, and biotite or hornblende are typically set in an aphanitic to glassy light to intermediate...
to rhyolitic
Rhyolite
This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
s and lapilli
Lapilli
Lapilli is a size classification term for tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. Lapilli means "little stones" in Latin. They are in some senses similar to ooids or pisoids in calcareous sediments.By definition lapilli range...
tuffs. The caldera complex lies in the Wabigoon greenstone belt.
The Sturgeon Lake Caldera contains volcanic units that outcrop over 30 kilometers from east to west with up to five separate, major ash flow tuff units with thickness ranging from 100 m (328 ft) to 1200 m (3,937 ft). The Mattabi pyroclastic flow, with a thickness in excess of 800 m (2,625 ft) and a strike length of at least 30 km (19 mi), is the third and most voluminous eruptive event associated with the Sturgeon Lake Caldera. It hosts the 12-Mt Mattabi massive sulfide deposit
Volcanogenic massive sulfide ore deposit
Volcanogenic massive sulfide ore deposits are a type of metal sulfide ore deposit, mainly Cu-Zn-Pb which are associated with and created by volcanic-associated hydrothermal events in submarine environments....
which is interpreted to have formed on and below the seafloor, the latter through the processes of pore-space filling and replacement.
See also
- Volcanism of Canada
- Volcanism of Eastern CanadaVolcanism of Eastern CanadaVolcanism of Eastern Canada has led to the formation of hundreds of volcanic areas and extensive lava formations, indicating volcanism played a major role in shaping its surface. The region's different volcano and lava types originate from different tectonic settings and types of volcanic...
- List of volcanoes in Canada