Yellowknife: The Canadian Shield & Greenstone Belt EarthCache
Yellowknife: The Canadian Shield & Greenstone Belt
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Precambrian Shield
The Canadian Shield is part of the Precambrian Shield, which is a structural unit of the Earth's crust composed of exposed basement rocks formed during the Archean or Proterozoic eons which together comprise the Precambrian Era ending 544 million years ago. Originally formed during mountain-building activity, Shield rocks are now among the most stable on Earth.
Canadian Shield
The Canadian Shield covers approximately 4.8 million square kilometres. It extends north to the arctic archipelago and south to the states of Wisconsin and New York, and east to west from Labrador to the western Northwest Territories.
The Precambrian mountains that long ago would have covered Yellowknife have been eroded away by glacial activity, which has created the low, rolling rock plain you can see around Yellowknife today. The glacial ice also resulted in the countless lakes, rivers, streams and ponds found around Yellowknife.
There are many areas around Yellowknife where you can find exposed shield rocks (behind you is one of them). Most of the rocks you will likely see are Basalt. Basalt is typically grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its iron-rich minerals into rust. The name comes from the green hue imparted by the colour of the metamorphic minerals within the mafic rocks.
Greenstone Belt
Yellowknife sits on a greenstone belt, also known as the Yellowknife Volcanic Belt.
The greenstone name comes from the green hue imparted by the colour of the metamorphic minerals within the rocks (there is some very noticeable greenstone rock just north of Yellowknife, along Ingraham Trail on the left side before you get to Giant Mine, if you are traveling north). This specific section of the greenstone belt is known as the Kam Group, which is a 10 km (6 mi) thick Archean volcanic group in the Yellowknife greenstone belt.
The Yellowknife Greenstone Belt is mostly made of mafic (rich in magnesium and iron) volcanic rocks (basalt and andesite).
To log this earthcache, you will first have to email me the answers to the following questions and post the optional photo with your log.
First, email me the answers to the following questions:
1) On the information board located at the coordinates it states that there are other similar shields of old rock on other continents, how do they differ from the shield rock found around Yellowknife?
2) Go to the shield rock visible behind you, or another area along Frame Lake Trail, or around Yellowknife, and describe the appearance of the rock (colour, texture, mineral size (if any), etc.) Do you think this rock is Basalt, explain why.
3) What type of rock do you think the majority of the Canadian Shield around Yellowknife is (igneous, sedimentary, or metamorphic)?
4) While walking along the trail to the cache coordinates, did you notice any of the Greenbelt rock that can be found in areas around Yellowknife? If so, describe it.
5) (Optional question) You will most likely have noticed a greenish-yellow lichen growing on the shield rock all over Yellowknife, what is the name of this lichen? (check the information board)
Also another optional requirement is to post a photo you have taken at the location or somewhere around Yellowknife of some Canadian Shield or Greenstone rock. (you being in the photo is also optional)
Information provided by:
http://www.thecanadianencyclopedia.com/articles/shield
http://en.wikipedia.org/wiki/Canadian_Shield
http://en.wikipedia.org/wiki/Yellowknife_greenstone_belt
Additional Hints
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