Buffalo Head Terrane facts for kids

The Buffalo Head Terrane (BHT) is a huge piece of Earth's crust. It's found deep underground in northern Alberta, Canada. This area is part of the western Canadian Shield. The BHT is covered by about 1,600 meters (that's over a mile!) of younger rocks. These rocks formed during the Devonian and Cretaceous periods. In the middle of the BHT, you can find special rocks called kimberlites. These kimberlites are about 86 to 88 million years old. They are part of the Buffalo Head Hills kimberlite province, which is famous for its diamonds!

What is the Buffalo Head Terrane?

Because the Buffalo Head Terrane (BHT) is hidden under many layers of rock, we can't see it directly. Scientists learn about it using special tools. They use aeromagnetic surveys, which are like giant magnets that map the Earth's magnetic field. They also use drill cores, which are long samples of rock taken from deep underground.

Where is the BHT located?

The exact size of the BHT is still a bit of a mystery. We know its edges are defined by other big geological features:

• To the south, it ends at the Snowbird Tectonic Zone.
• To the north, it's bordered by the Great Slave Lake Shear Zone.
• In the east, it's separated from the Rae Craton by the Taltson Magmatic Zone. This zone formed about 1.9 to 1.99 billion years ago.
• To the west, it's separated from the Nova Terrane by the Ksituan High, which is made of volcanic rocks.

In its southern part, the BHT is also affected by the Peace River Arch. This is a large area of the Earth's crust that has been slowly lifting up for a very long time.

How old is the BHT?

Scientists like Ross, who studied the BHT in 1990, looked at the magnetic patterns in the area. They found that the BHT is a wide region with a north-south direction. By studying rock samples from drill cores, scientists found tiny crystals called Zircons. These crystals showed that the BHT rocks are very old, ranging from 1.993 to 2.324 billion years old. Some of the rocks, called metaplutonic rocks, formed about 1.993 to 1.999 billion years ago. This suggests that the BHT itself formed between 2.0 and 2.32 billion years ago. It was then affected by a period of heat and magnetic changes about 1.9 to 2.0 billion years ago.

How did the BHT form?

The very old rocks (called basement rocks) in the BHT are about 2.1 to 2.4 billion years old. The nearby Rae Craton has rocks of a similar age and chemical makeup. This makes scientists think that the BHT and the Rae Craton were once connected, forming one big piece of crust about 2.4 billion years ago. However, around 2.34 billion years ago, some volcanic rocks formed between the BHT and the Rae Craton. This suggests they started to separate around that time. Later, the BHT was pushed down under other plates at its eastern and western edges. This process is called subduction. This pushing down caused a lot of volcanic activity, creating the volcanic arcs we now see as the Taltson Magmatic Zone (1.92 to 1.98 billion years ago) and the Ksituan High (1.9 to 1.986 billion years ago).

Diamond-Rich Kimberlite Field

The Buffalo Head Hills kimberlite field is a special place where diamonds are found. It's a bit unusual compared to other diamond areas.

Why is this diamond field unique?

Most diamond deposits have certain "indicator minerals" like a type of garnet called harzburgitic garnet. But in the Buffalo Head Hills, these minerals are rare. This suggests that the rocks deep in the Earth's mantle, where these diamonds formed, are different here. Also, this area has unusual types of diamonds, called Type II and Type IaB diamonds. These types of diamonds often form very deep inside the Earth, perhaps from an oceanic plate that was pushed down (subducted) into the mantle. Another type of garnet found here, called lherzolitic garnet, suggests that these diamonds formed at an incredible depth of about 400 kilometers (250 miles) below the surface!

How many diamonds are there?

Even though it's an unusual place, 26 out of the 38 kimberlite pipes in the Buffalo Head Hills kimberlite field contain diamonds! These kimberlite pipes are like carrot-shaped tunnels that go deep into the Earth. They can be quite large, ranging from 1 to 47 hectares (about 2.5 to 116 acres) in size at the surface. Drilling has only explored the top 200 meters (about 650 feet) of these pipes so far.