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Xenoliths From the Mantle- Little Green Rocks From Deep Inside the Earth

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?...

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.

Ken Sims looking at mantle xenoliths near the summit of Mount Terror with the East Ridge in the background. This East Ridge is where we have been sampling for the past two weeks. Photograph by Erin Phillips Writer
Plate 2: Picture of mantle xenoliths in outcrop at a lava flow on the East Ridge of Mount Terror. Photograph by Paul Wallace

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.

Picture of mantle xenolith in the laboratory. Green crystals are olivine and black crystals are pyroxene. Photograph by Paul Wallace

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.

Woods Hole Oceanographic Institution scientist Glenn Gaetani in the ice cave in the Erebus Glacier Ice Tongue. Photograph by Ken Sims

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.

Hexagonal ice crystal in the Erebus Glacier Ice Tongue. Note hand for scale. Photograph by Alasdair Turner

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Meet the Author

Kenneth W W Sims
A Professor at the University of Wyoming and a former tenured Research Scientist at Woods Hole Oceanographic Institution, Dr. Kenneth W.W. Sims uses isotopic and chemical tracers to study geologic processes in the earth and other planetary bodies. Ken has over fifty peer-reviewed scientific publications focusing on the study of mantle melting, oceanic and continental crustal genesis, volcanology, hydrology, planetary core-formation, climate change and oceanography. Dr. Sims earned his BA in Geology from Colorado College, his MSc from the Institute of Meteoritics at the University of New Mexico; and his PhD in Geochemistry from the University of California, Berkeley. Ken’s field experience ranges from ocean floor geology, using submersibles and remote sensing techniques to geological studies of active volcanoes at high altitudes in technical terrain. Academic awards include: the Estwing Outstanding Senior Award at Colorado College, an Outstanding Student Instructor Award from the UC, Berkeley, the Woods Hole Oceanographic Institution Postdoctoral Scholar Fellowship, three Mellon Awards for innovative exploratory research and the Kincaid School 2012 Papadopoulos Fellowship. In addition to his academic career, Ken is an avid climber and has been an alpine guide for over three decades with extensive experience in technical, high altitude and cold weather mountaineering in Antarctica, the Alaska Range, and the Andes of Peru. These technical climbing skills have enabled him to collect young lavas and gather volcanic gas data inside active, remote volcanoes across the globe, including Erebus Volcano in Antarctica; Masaya Volcano in Nicaragua; and Nyamuragira and Nyiragongo Volcanoes in DR Congo. Using isotopic and geochemical data measured in these hard-to-get-samples Professor Sims’ ultimate goal is to better understand the genesis and evolution of Earth’s volcanoes, with an eye toward predicting future eruptions. Sims’ research and scientific expeditions have been featured in National Geographic Magazine; Oceanus; Popular Mechanics; New Scientist; several children’s books and magazines; NHK Japanese Public Television (Miracle Continent Antarctica- Mt Erebus), National Geographic Television (Man versus Volcano); and, the Discovery Channel (Against the Elements). Professor Sims is a featured scientist on National Geographic Explorer Site For Professor Sims’ complete Curriculum Vitae, Publication List and Mountaineering Resume see