The Building of British Columbia, Canada

For people, a hundred years seems like a long time, and incredible changes have taken place in the last one hundred years. But geologically, not much changes in one hundred years. Humans have drastically changed the Earth’s surface, and not so much in a good way. The changes made geologically can take tens to hundreds of millions of years for obvious changes, but all the same, the Earth is in constant change. This is done through the processes of plate tectonics and weathering. The Earth is about 4.6 billion years old and has changed drastically from then. British Columbia is a great example to use because as of about 200,000 million years ago much of it didn’t exist.

The Earth in the beginning was so hot that there were no continents or even crust. It was a hot mess of gases and dust made up of chemical elements. Add gravity into this mess and asteroid bombardments and the Earth started forming into what we see today. Heavy elements like the metal elements iron and nickel got pulled down to the core of the planet, while lighter elements migrated upward towards the surface of the planet, like oxygen, silicon, and aluminum. These three elements are the most abundant elements in the mantle and crust. Slowly over time the Earth started to cool and the outer layer started to solidify and the atmosphere developed. Today, the Earth is still hot enough inside to cause the plates to continue moving. It is believed that eventually the Earth will cool enough that the plates will stop moving, but that will be billions of years away. Today, there are 15 to 20 moving tectonic plates. The slowest is the Arctic Ridge moving less that 2.5 cm (1 inch) per year to the fastest moving plate East Pacific Rise at more than 15 cm (5.9 inches) per year. Here in British Columbia, the North American plate is moving West / Southwest about 2.3 cm (1 inch) per year and the Pacific plate is moving Northwest about 7 to 11 cm (3-4 inches) per year, sliding passed and into each other. The Juan de Fuca plate (a fragment of the Farallon Plate) is sandwiched in between these two plates moving East / Northeast about 4 cm (1.6 inches) per year and is slowly disappearing under the North American plate. Plates collide on some sides (convergent boundaries), spread apart from one another on other sides (divergent boundaries), and can slide past each other (transform boundaries).

British Columbia is part of the North American plate, but it was not always as we see it today. North America has some of the oldest rocks on Earth, and dates back to be 4.28 billion years old in Quebec held within the Canadian Shield, which is part of an ancient continent called Laurentia. The continent has been pulled apart and added to over millions of years. Back about 1 billion years ago there was a super continent created called Rodinia that broke apart about 750 million years ago, and then about 335 million years ago reformed into a super continent again called Pangea. Both times, they were surrounded by a super ocean. Pangea began breaking up about 175 million years ago and the tectonic plates have been bumping into each other, moving away from each other, some plates completely disappeared by being subducted under other plates (usually ocean plates subducting under continental plates), and sliding past each other. The part where British Columbia eventually came to be, has been torn apart from the continent (creating the peri-laurentian terranes) creating Slide Mountain Ocean, closing again with parts twisted down southward, and then moving eastward, and various other plates with volcanic islands colliding into the North American plate accreting the terranes (continental fragments and ocean islands) to the westside of the continent.

The Major Geological Belts in the Building of British Columbia. From the book “Geology of British Columbia – A Journey through Time”

The Northeast corner of BC is a piece of the undeformed part of the North American continent called the Interior Plains. The Rocky Mountains are part of the original North American plate that was mostly sedimentary rock that was push up into the mountain range and called the Foreland Belt. The Omineca Belt is where the Intermontane plate with its terranes of volcanic islands collided with the North American plate welding the two parts together. This is an area with metamorphosed rocks. This was once a subduction zone. The Intermontane Belt is the various terranes of the Intermontane plate that became part of the North American plate.

By Black Tusk – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=5736724
 

The Coast Belt is where the Insular plate with its volcanic islands collided with the Intermontane plate (that was accreted to the North American plate by then) and was accreted to the Intermontane plate, also becoming part of the North American plate. Behind the Insular plate was the Farallon Plate being subducted under the Insular plate. The Insular plate is the most western part of British Columbia which includes a small part of the coastline, Vancouver Island, and Haida Gwaii. Today, we have a piece left of the original Farallon plate, now called the Juan de Fuca plate subducting under the Insular plate (that is now part of the North American plate). This is an area of tension between the two plates that will eventually give and cause an earthquake. Eventually, the Juan de Fuca plate will disappear completely.

By Black Tusk – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=5739509

References:
Geology of British Columbia, A Journey Through Time by Sydney Cannings, Joanne Nelson, and Richard Cannings
https://pubs.usgs.gov/gip/dynamic/understanding.html
Wikipedia.org

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