The Big Dan Shear Zone is a north–south trending

shear zone In geology, a shear zone is a thin zone within the Earth's crust or upper mantle that has been strongly deformed, due to the walls of rock on either side of the zone slipping past each other. In the upper crust, where rock is brittle, the shear ...

Northeastern Ontario Northeastern Ontario is a secondary region of Northern Ontario in the Canadian province of Ontario, which lies north of Lake Huron and east of Lake Superior. Northeastern Ontario consists of the districts of Algoma, Sudbury, Cochrane, Timisk ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

, located in the municipality of

Temagami Temagami, formerly spelled Timagami, is a municipality in northeastern Ontario, Canada, in the Nipissing District with Lake Temagami at its heart. The Temagami region is known as ''n'Daki Menan'', the homeland of the area's First Nations com ...

Geology

The Big Dan Shear Zone was contemporaneous to

volcanism Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of a solid-surface astronomical body such as a planet or a moon. It is caused by the presence of a he ...

due to the higher density of

felsic In geology, felsic is a grammatical modifier, 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 ...

dikes Dyke or dike may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), formations of magma or sediment that cut through and across the layering of adjacent rocks * Dike (mythology), ''Dikē'', the Greek goddess ...

situated at the shear zone. These dikes are only present north of the Link Lake Deformation Zone, therefore they may be subvolcanic feeders to the felsic lava flows to the south. Renewed

tectonism Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...

along the Big Dan Shear Zone displaced

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s east of the

Ontario Northland Railway The Ontario Northland Railway is a Canadian railway operated by the Ontario Northland Transportation Commission, a Crown agency (Ontario), provincial Crown agency of the government of Ontario. Originally built to develop the Lake Timiskaming ...

. This phase of tectonic activity along the Big Dan Shear Zone also displaced felsic dikes north of the

. However, considerable displacement of the dikes at this location is unknown. The most recent tectonic activity of the Big Dan Shear Zone displaced a

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 ...

dike composed of

diabase Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-gra ...

, which intersects the zone. A similar abundance of felsic dikes are adjacent to Arsenic Lake just west of Highway 11, indicating that similar

also occurred along that structural zone. Therefore, these north-trending shear zones may have been tectonically active for at least a billion years.

References

Structural geology Geologic faults of Temagami Strathy Township Shear zones {{struct-geology-stub