Sturgeon Lake Caldera is a large

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

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 ...

complex in

Kenora District Kenora District is a district and census division in Northwestern Ontario, Canada. The district seat is the City of Kenora. It is geographically the largest division in Ontario: at , it covers 38 percent of the province's area, making it larger ...

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 ...

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 ...

. It is one of the world's best preserved mineralized Neoarchean caldera complexes, containing well-preserved

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 ...

-intermediate

pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of discont ...

s, pillow

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

s, hyaloclastite and

peperite A peperite is a type of volcaniclastic rock consisting of sedimentary rock that contains fragments of younger igneous material and is formed when magma comes into contact with wet sediments. The term was originally used to describe rocks from th ...

s, submarine

lava dome In volcanology, a lava dome is a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions ...

s and dome-associated breccia deposits. The complex is some 2.7 billion years oldCaldera Volcanoes
Retrieved on 2007-07-20 with a minimum strike length of .

Geology

The Sturgeon Lake Caldera contains a well preserved north facing homoclinal chain of

greenschist facies Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as chlorite, ...

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

intrusive,

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...

, and

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 ...

layers. This piecemeal caldera complex includes nearly of major subaqueously deposited intracaldera fill. Episodes of subaerial and subaqueous explosive

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 ...

volcanism created

rhyodacitic Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rapid ...

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The ...

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

s and

lapilli Lapilli is a size classification of tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. ''Lapilli'' (singular: ''lapillus'') is Latin for "little stones". By definition lapilli range ...

tuffs. The caldera complex lies in the Wabigoon greenstone belt. The Sturgeon Lake Caldera contains volcanic units that outcrop over from east to west with up to five separate, major ash flow tuff units with thickness ranging from to . The Mattabi pyroclastic flow, with a thickness in excess of and a strike length of at least , 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.

References

{{reflist
CAT.INIST - Sturgeon Lake Caldera Complex

External links

Oxygen Isotope Studies of the Archean Sturgeon Lake Caldera Complex, Northern Ontario
Calderas of Ontario Complex volcanoes Archean calderas Lava domes VEI-6 volcanoes Polygenetic volcanoes Landforms of Kenora District Neoarchean volcanism

Geology

See also

References

External links