Scientists from the British Antarctic Survey have made a breakthrough in solving a decades-old geological mystery by identifying a large granite mass buried beneath the West Antarctic Ice Sheet (WAIS). The team discovered the mystery after noticing some exotic (pink) stones located at the top of a black volcano within the Hudson Mountains. Next, they conducted state-of-the-art aerial gravity surveys and modern radiometric dating to establish how these ‘irregular’ boulders were tied to the huge, magmatic Jurassic-aged granite body (the ‘hidden giant’), which measured 100 kilometers across and covered a surface area almost half the size of Wales, extending to 7 kilometers depth beneath Pine Island Glacier. The incredible hardness of the hidden giant will also greatly influence the flow rate of sea ice, providing a new factor in the knowledge base used to predict global sea level rise due to the rate of ice melting around the world.
Origin of 175 million year old rocks found in Antarctica
It all started with a geological anomaly in the Hudson Mountains of West Antarctica, where exotic pink granite boulders were found on top of deep volcanic peaks. The pink granite boulders (‘irregular’) did not resemble the surrounding volcanic rock in any way and after much debate, scientists concluded that these boulders were ‘uprooted’ from the valley floor by a fairly thick ancient ice sheet and then deposited on top of the volcanic peaks when the ice receded. According to research published in Nature, using U-Pb zircon geochronology (radioactive dating), scientists determined that these rocks were about 175 million years old, dating back to the Jurassic period, when the supercontinent Gondwana began to break up.
How scientists discovered a 100-km-long granite mass beneath Antarctic ice
Because the source of the pink rocks was buried under miles of ice, the British Antarctic Survey used aerial geophysical surveys by flying Twin Otter aircraft equipped with geophysical instruments to conduct both gravity and magnetic surveys on Pine Island Glacier to define the density of the materials beneath. Ultimately, they discovered a giant granite body, or ‘pluton’, approximately 100 kilometers wide and 7 kilometers thick; The approximate area of the granite body is half that of Wales. This large block of granite is significantly harder and more stable than the surrounding sedimentary basins.
Why is the West Antarctic Granite Body important to climate models?
The discovery is important not only because of its geological significance, but also because it will impact climate science. Pine Island Glacier, one of the fastest melting glaciers in Antarctica, is one of the largest contributors to global sea level rise. The ‘hidden giant’, or the world’s largest granite formation, provides the bedrock support or structural skeleton for the ice sheet. Since granite is an exceptionally dense and hard bedrock, this would be a high-friction site where the glacier would grip the ground more tightly or create ‘sticky’ points in some places, slowing the movement of the glacier into the sea. The exact size and position of this granite structure will be a key variable in computer models that predict how much sea level rise will occur in the year 2100.
Granite bodies are a ‘missing link’ in Earth’s history
Furthermore, this granite body provides a glimpse of the history of Gondwana. According to a research paper published on USGS, the chemical composition of the granite boulders indicates that they were formed during a time of intense tectonic activity and rifting, thus providing geologists a more complete record of the ‘missing link’ in the West Antarctic Rift System. This confirms that this location was once an area of large amounts of magma that was injected into the Earth’s crust and cooled beneath the surface before being covered by the West Antarctic Ice Sheet millions of years ago.