Written by Kenneth W W Sims
We are familiar with the geology we see on the surface of the Earth—the granite cliffs of Yosemite, the volcanoes of Hawaii, Yellowstone and Mount Saint Helens, or the red sandstone spires in the deserts of the American southwest. But what does deep inside of the Earth look like? As geologists we have many different methods to discern the composition and structure of the Earth’s mantle indirectly and sometimes we are lucky enough to find samples of the mantle transported up to the surface by volcanic lava flows.
One of the cool things about working in remote settings like Antarctica, where there are locations no geologist has ever before explored, is that you get to make exciting discoveries. One of those discoveries for us has been finding lots of “mantle xenoliths” along the East Ridge of Mt Terror (Plate 1 and 2). These mantle xenoliths (which means foreign rock in Greek) are made up of beautiful green olivine and black pyroxene crystals (Plate 3). Mantle xenoliths represent the deep mantle below the crust (~20- 100 kms deep) that is being melted to form the magmas of the Ross Island volcanoes. We find them in cinder cones and sometimes in the lava flows; the green xenoliths are round nodules that stand out in stark contrast to the black and dark gray lava.
Next we are off to camp at Cape Bird to start sampling along the coast and on the summit of Mt Bird. This should be another exciting part of the trip, as once again there are very few samples that have been collected from Mt Bird and we will also be camping next to a penguin rookery.
Some other good news is that Glenn Gaetani, who was delayed in Woods Hole on account of Hurricane Sandy, has made it to Antarctica. Our team is now complete. So yesterday to get Glenn oriented and ready to sample we did a snowmobile tour on the sea ice along Hut Point Peninsula , which included sampling at Turtle Rock and an essential side trip to the nearby ice cave on the Erebus Glacier tongue (Plate 5). Glenn will be writing the next blog from Cape Bird – so stay tuned.