Geology of Ontario hiking trails takes you back in time.

Test Post Ontario

-tectonic plates began moving 3 bya, most of which were ocean plates
-two ocean plates crossing in subduction zone, create volcanism, island arcs, build continental crust
-heavier ocean plate goes under continental plate but some ocean crust scraped & piled up on continent
-Canadian Shield is the world’s biggest craton, grew by accretion
-sediments and island arcs swept against craton’s size, creating various terranes welded to each other
-3 Geological Provinces from oldest to youngest and sedimentary basins:
Surperior 2.5-3.8 bya: 9 greenstone meta-volcanic & granite, 2 sedimentary, 1 granitic belts
Southern 0.57-2.5 bya: flat lying seds at Elliot Lake 2.25 bya & Lake Huron, Thunder Bay 1.54bya
Grenville 0.57-1.0 bya: northern part is mainly gneiss, southern is meta-volcs, -seds, plutons
Paleozoic & Mesozoic Basins 63-570 mya: thick layers of limestone, shale, sandstone

 

ARCHEAN 2.5 to 4.6 bya

-mainly oceans covered Earth, with very small early cratons
-volcanism on land and underwater spewing lava, ash, gas
-air mainly carbon dioxide & nitrogen, no free oxygen, no ozone
-very hot, only life tiny algae and bacteria that lived in sea

-oldest rocks around Red Lake, dating 3.25 bya
-volcanoes spread lava from east to west, creating several volcanic island arcs
-these island arcs eventually collided with edge of young Ontario
-volcanic islands eroded by powerful currents, depositing sediments along edge of craton
-process repeated 3 times
-final stage when island arcs and basins collided into craton, creating mountains as high as Rockies
-colliding plates heated and compressed volcanic and sedimentary rocks, creating metamorphic rocks
-collision also caused magma to rise up, further heating rocks and creating granite batholiths underneath

SURPERIOR PROVINCE ………………12 geological subprovinces separated from one another by faults

Granite-Greenstone Subprovince
-former volcanic island arcs between 2.7-3.2 bya
-9 narrow belts of meta-volcanics with younger granite batholiths
-4 rock assemblages: platform, arc, mafic plain & wrench basin
Platform: komatiite, shale & iron formation, qz-rich seds (top to bottom, 2.85-2.99 bya)
-Steep Rock, Lumley Lake assemblage in Wabigoon subprovince
Arc: thin layer volcanic ash, rhyolite bombs & breccias over thick basaltic flows
-underwater flows followed by explosive eruptions as oceanic & cont plate collided
-Rottenfish, Catfish, Pickle Crow; oldest is 3.02 bya near Red Lake
Mafic Plains: basalt or komatiite within sediments, such as black shale 2.70-2.77 bya
-underwater volcanoes like Hawaii, with smooth pahoehoe and clinkery a’a flows
-only a few locations, such as Hawk assemblage near Wawa
Wrench Basins: coarse seds & volc rocks found in basin surrounded by active faults
-lie on top of older, very weathered greenstones
-late stage collision of island arc & ocean plate
-seds & pieces of sea floor scraped off and piled up against island arc, forming basin
-collision triggers volcanism which stops when island arc and sed basin jam together -fault marks boundary where island arc and basin are joined
-gold mines are found near these faults – Timmins, Kirkland Lake, Shebandowan

Sedimentary Subprovince
-2 subprovinces, Quetico & English River, formed 2.66 & 2.72 bya
-sedimentary rocks, mainly greywacke, with some conglomerate and siltstone
-deposited by strong underwater turbidity currents (underwater avalanches due to plate collisions)
-prism shaped deposits of seds into basins along edge of young Ontario

Plutonic Subprovince
-only one, the Winnipeg River Subprovince
-plutonic granite that is baked and squeezed by plate action into gneiss 2.68 bya

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