Approximately 1.268 billion years ago, the Earth looked like a completely alien planet.
Part of earth's oceans may have been purple near the equator due to an abundance of sulfur
eating bacteria.
Plants had not yet evolved, so the abundant continents that were present were colored
a mixture of gray and white from exposed bedrock and snow.
And, during the planet's 18 hour days, the center of volcanic activity at the time was
in what is now far northern Canada.
There, large floods of basaltic lava poured onto the surface, burying large swaths of
land in up to 3500 meters thick of molten rock.
During a 2 million year long period, 2.7 million square kilometers of land ranging from Ontario
to the Northwest Territories experience voluminous eruptions.
This large igneous and flood basalt sequence is today referred to as the Mackenzie dike
swarm.
The reason for this name is the large radiating dikes it left throughout the landscape, which
all seemingly point toward the swarm's center.
This dike system is the largest on the planet, and represents the solidified molten rock
below where large fissure eruptions occurred.
For context, a dike is a tabular or sheet like body of magma that cuts through and across
the layering of adjacent rocks.
Dikes are quite common at volcanoes, but in the case of unusually large systems such as
calderas they often radiate outwards from a central point.
For example, the ancient igneous intrusion known as Shiprock in New Mexico has a series
of such dikes which radiate outwards from what was once its central magma chamber.
The Mackenzie dike swarm began erupting 1.268 billion years ago, when the head of a large
mantle plume centered underneath Victoria Island permeated through the crust.
However, significant lava did not erupt there as the crust was too thick.
Instead, the magma was funneled towards the south where the crust was thinner, eventually
erupting onto the surface via a magnificent sequence of fissure eruptions.
Dozens if not hundreds of fissure eruptions began near simultaneously, which recent data
suggesting that this initial phase even caused volcanism in Yukon at the Bear River dikes.
Each of these fissures output thousands of cubic meters per second of basaltic lava,
which quickly flowed over the landscape.
It is easiest to picture each of these flood basalts as 500 simultaneous eruptions of the
Geldingadalir volcano in Iceland.
These eruptions lasted for decades, sending lava flows up to 350 kilometers distant and
depositing thousands of cubic kilometers of rock.
The center of activity occurred near the Coppermine River, where the thickest and most voluminous
flood basalts erupted.
Over the span of 2 million years, 500,000 cubic kilometers of black basaltic rock was
emplaced here.
The underlying mantle plume which fed this volcanism was 1000 kilometers wide, and this
fact is known due to the orientation of the numerous dikes.
While dikes were vertical or near vertical within the boundary outlined on screen, they
were horizontal outside of this radius.
Volcanism began decreasing by 1.267 billion years ago, and stopped altogether by 1.266
billion years ago as the underlying hotspot no longer provided sufficient volumes of molten
rock to continue constant eruptions.
These voluminous eruptions permanently changed the overall landscape, as 650,000 cubic kilometers
of molten rock was erupted, potentially more.
One notable feature of economic interest was a large magma chamber which was active during
this period that was spread out over an area of greater than 100 square kilometers.
This ancient magma chamber held 10,000 cubic kilometers of molten rock, and contained unusually
high concentrations of minerals rich in palladium, platinum, gold, nickel, and copper.
Copper often occurred as large nuggets of material, whose abundance would later be used
to name the Coppermine River.
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