British Antarctic Survey scientists have made a breakthrough in understanding a decades-old geographical mystery by identifying a large granite body buried beneath the West Antarctic Ice Sheet (WAIS). The team discovered the mystery after noticing some strange (pink) boulders atop a black volcano in the Hudson Mountains. They have since carried out state-of-the-art airborne gravity surveys and modern radioactive dating to determine how these “unstable” boulders are linked to a massive Jurassic magmatic granite body (the “hidden giant”), which is 100 kilometers in diameter, covers a surface area about half the size of Wales, and extends to a depth of 7 kilometers beneath Pine Island Glacier. The incredible stiffness of this hidden giant will also greatly affect the rate at which ice flows to the ocean, adding a new factor to the knowledge base for predicting global sea level rise as a result of global ice melt rates.
The origin of 175-million-year-old rocks discovered in Antarctica
It all started with a geological anomaly in the Hudson Mountains of West Antarctica, where a massive collection of bizarre pink granite boulders were discovered on the dark volcanic peaks. These pink granite boulders (“unstable”) bear no resemblance to the surrounding volcanic rocks, and after much debate, scientists concluded that the boulders were “plucked” from the valley floor by thicker ancient ice sheets and then deposited on the volcano’s summit as the ice retreated. According to research published in the journal Nature, scientists used U-Pb zircon geochronology (radioactive dating) to determine that the rocks are about 175 million years old, dating back to the Jurassic period, when the supercontinent Gondwana began to break apart.
How scientists discovered a 100-kilometer-long granite body beneath the Antarctic ice
Because the source of the pink rock is buried under miles of ice, the British Antarctic Survey used airborne geophysical surveys, flying a Twin Otter aircraft equipped with geophysical instruments, to conduct gravity and magnetic surveys on Pine Island Glacier to determine the density of the material below. Eventually, they discovered a huge granite body, or “rock mass,” about 100 kilometers wide and 7 kilometers thick; it’s about half the size of Wales. This large piece of granite is harder and more stable than the surrounding sedimentary basin.
Why West Antarctic granite bodies are key to climate models
This discovery is important not only because of its geological significance, but also because it will impact climate science. Pine Island Glacier is one of Antarctica’s fastest melting glaciers and one of the largest contributors to global sea level rise. The “hidden giant,” the world’s largest granite formation, provides the basic support, or structural skeleton, of the ice sheet. Because granite is an unusually dense and hard bedrock, it would be a high-friction site where the glacier would grip the ground more tightly or create “sticky” spots in places, slowing the glacier’s movement toward the ocean. The exact shape and location of this granite formation will become a key variable in computer models used to predict how much sea levels will rise by 2100.
Granite bodies are the ‘missing link’ in Earth’s history
Additionally, this granite body provides a glimpse into the history of Gondwana. The chemical composition of the granite boulders suggests they were formed during periods of intense tectonic activity and rifting, providing geologists with a more complete record of the “missing link” in the West Antarctic rift system, according to a research paper published by the U.S. Geological Survey. It confirms that the site was once a region with vast amounts of magma that was injected into the Earth’s crust and cooled below the surface before being covered by the West Antarctic Ice Sheet millions of years ago.
