Scientists from the British Antarctic Survey 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 came upon the mystery after noticing some exotic (pink) boulders located on top of black volcanics within the Hudson Mountains. Following this, they conducted state-of-the-art airborne gravity surveys and modern radiometric dating to establish how these ‘erratic’ boulders were tied to the massive, magmatic Jurassic-aged granite body (the ‘hidden giant’), which is measured at 100 kilometres across and covers a surface area roughly half the size of Wales, extending 7 kilometres deep below the Pine Island Glacier. The hidden giant’s incredible hardness will also greatly affect ice flow rates to the ocean, thereby providing a new factor in the knowledge base used to predict global sea level rises due to ice melt rates worldwide.
The origin of the 175-million-year-old rocks found in Antarctica
This all started with a geological anomaly in the Hudson Mountains of West Antarctica, where substantial to exotic pink granite boulders were found on top of dark volcanic peaks. The pink granite boulders (‘erratics’) were not in any way similar to the surrounding volcanic rock and after much debate, scientists concluded that these boulders were ‘plucked’ off the valley floor by a substantially thicker ancient ice sheet and then deposited on top of the peaks of the volcano as the ice receded. According to the research published in Nature, using U-Pb zircon geochronology (radioactive dating), scientists determined that these rocks were approximately 175 million years old, dating from the Jurassic Period when supercontinent Gondwana began to break apart.
How scientists discovered a 100-kilometre granite body beneath Antarctic ice
Because the source of the pink rocks was buried under miles of ice, the British Antarctic Survey used airborne geophysical surveys, flying a Twin Otter aircraft equipped with geophysical instruments, in order to conduct both gravity and magnetic surveys over Pine Island Glacier in order to define the density of the materials below. Ultimately, they discovered an enormous granite body, or ‘pluton’, that is approximately 100 kilometres wide and 7 kilometres thick; the approximate area of the granite body is half of Wales. This large block of granite is significantly harder and more stable than the surrounding sedimentary basins.
Why the West Antarctic granite body is key to climate models
This discovery is important not only because of its geological significance, but also because it will impact climate science. The 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 base support or structural skeleton for the ice sheet. Since granite is an exceptionally dense and rigid bedrock, it will be a high-friction site where the glacier will grip the ground more tightly or cause a ‘sticky’ point in some places, thereby slowing down the movement of the glacier into the ocean. The exact shape and position of this granite formation will be a key variable in computer models that predict how much sea level rise there will be in the year 2100.
The granite body is a ‘missing link’ in Earth’s history
In addition, this granite body provides a glimpse into the history of Gondwana. According to the 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 with a more complete record of the ‘missing links’ in the West Antarctic Rift System. It confirms that the location was once an area of large volumes of magma that was injected into the Earth’s crust and cooled below the surface before it was covered up by the West Antarctic Ice Sheet millions of years ago.
