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Home , McMurdo Dry Valleys

Travelogue The Roots of a Flood Province: Expedition to

Jean H. Bédard Natural Resources Canada, Québec In January 2005, I participated in an Antarctic field mapping workshop with a group of researchers under the leadership of Bruce Marsh (Johns Hopkins University), who had obtained a generous grant from the National Science Foundation (Office of Polar Programs, Geology and Geophysics) covering all field and travel expenses. The focus was the plumb- ing system feeding the continental flood that erupted when the South Atlantic Ocean opened 185 million years ago (Kirkpa- trick Basalts, Ferrar Dolerites, Dufek Intrusion). Flood basalts are important features of the geological record, and their emplacement is one of the mechanisms proposed for mass Group photo taken at McMurdo Station. Front row Sam Mukasa, Dougal Jerram, Taber Hersum. 3rd row: (L to R): Andrew Feustel, Dennis Geist, Tom Fleming, extinction. The subvolcanic intrusions that Karen Harpp, Jean Bédard, Michael Garcia, Dick Alan Boudreau, Dave Elliott, Jill van Tongeren, Justin Naslund, Adam Simon, Bruce Marsh. Not present: feed flood basalts are also important sources Durrell, Amanda Charrier. 2nd row: Jennifer Cooper, George Bergantz, Stu McCallum, Michael Manga, of nickel and platinum-group elements (e.g. Ron Fodor, Scott Paterson, Ed Mathez, Jon Davidson, Simon Katterhorn. Noril’sk). However, despite their importance, many issues about the genesis of cumulate postcumulus textural and chemical reequili- rocks remain unresolved. The origin of cumu- bration, which largely obliterates the evidence late rocks being one of my principal interests, of the early processes, making it difficult to the trip prospectus, published in EOS, decipher how cumulate rocks and associated attracted my attention. With my employer’s ore deposits form. blessing I applied, and was very pleased to be Travel to Antarctica requires an intensive among those selected for the workshop. medical screening process, since evacuation is expensive and can be subject to long delays because of the weather. Extra-cold-weather gear is issued at the efficient US Antarctic Program’s clothing distribution centre in Christchurch, New Zealand. Our first attempt to reach “The Ice” aboard a US Military Air Command C-141 Starlifter failed due to inclement weather. A frustrating week of postponements followed, with a nightly 3 a.m. knock on the door of the “Bed and Breakfast.” The refrain of “24-hour delay” was greeted by curses and groans by those of us with tight schedules. Finally, the weather cleared, and after an The author in front of the Beacon at the Dais intrusion, , ~400 m thick. The pale uncomfortable eight-hour flight, we were head of Taylor . The icecap is visible behind material at the summit is basement. Note sitting on the Ross Ice Shelf, where McMurdo the icefalls. the pale subhorizontal layers, which correspond to Station is situated, looking at the smoking feldspar-enriched cumulates. In the foreground, orthopyroxenitic cumulates are sculpted by the wind. cone of Mount Erebus, an active alkaline “beakers”) fly in two or three times a week. volcano forming the spine of Ross Island. Helos (helicopters) are constantly taking off McMurdo (or Club Mac, as some call it) is the and landing, and in good weather, US and NZ The workshop was to target the mechanics of main US base, and its population swells from Hercules transports take off a dozen times a sill emplacement and the diversity of magma about 250 in winter to over 1000 scientists day to ferry fuel down to the Pole. differentiation mechanisms, including crystal and workers in the austral summer. McMurdo The first item on the agenda upon our arrival transport and sorting, deposition, postcumu- is situated at approximately 78oS, and in was an intensive cold-weather survival course, lus melt transfer, and assimilation of wall- January there are 24 hours of sunshine, which which included a night out in a Quonzie/Igloo. rocks. The plumbing system of the is somewhat disorienting when leaving the At –5°C, the weather was mild compared to flood basalts is extraordinarily well preserved pub at midnight. A lounge provided in each what I left behind in Canada (−30). After and exposed in the Dry Valleys of Antarctica block has all the amenities of home, including “graduating” we were authorized for deploy- (Marsh 2004). , dikes, and chilled mar- satellite TV, pool tables, washing machines, ment to our Dry Valleys camp. The Dry gins contain microphenocrysts that can serve etc. Food is served in a huge cafeteria-style Valleys receive essentially no precipitation, as points of comparison with the cumulate galley. There are a gym and three bars—one and the principal geomorphic process is the rocks occurring in the lowermost of three for beer-drinking smokers, one for beer- wind. Wind-blown dust carves the cliffs into feeder sills (300–500 m thick), in which the drinking non-smokers, and a café–wine bar weird, elephant-graveyard-like ventifacts. earliest stages of cumulate formation and for effete intellectuals. Most importantly, the maturation are recorded. In contrast, the long station boasts a superbly equipped laboratory. The environmental rules in Antarctica are cooling times of large layered intrusions like McMurdo is a veritable hive of activity in the very strict, and no waste of any kind is the Bushveld Complex allow extensive summer as plane-loads of scientists (known as allowed to touch the ground. This means that

E LEMENTS 316 DECEMBER 2005 Calendar

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we had to carry around a P-bottle all day, and on site. Life in camp was definitely more at the end of the day empty it into a big relaxed, since we were able to rise at a slothful orange P-drum. Our camp in was a 7 a.m. and walk to a well-exposed section. neat arrangement of tents clustered around a The research crew was a multinational herd main expedition tent that served as our of cats, and many lively debates took place kitchen and lounge. Unfortunately, we had to on the outcrop. Discussion concerned mecha- rotate between the camp and Club Mac, since nisms of layering development, and post- only half of our team could stay in camp at cumulus melt transfer within the orthopyrox- any one time in order to minimize our envi- enite zone of the Basement Sill. Several days ronmental footprint. This meant that the were occupied by excursions guided by Bruce other half of the crew had to fly out each Marsh and his students. Following these, we morning and return on a flight at night. On broke up into thematic subgroups. Finally, one occasion we had three successive days after almost two weeks in the field, it was when we rose at 6 a.m. to get our helo and time to go back to the real world. All in all, were picked up to return to McMurdo after the trip was a grand success and promises to 11 p.m. Returning to base after midnight be seminal with regard to the development resulted in 18-hour work days and a little of new concepts of magma chamber evolu- Ferrar dolerite sill, Finger Mountain, injected into Jurassic more than four hours sleep on those nights. Beacon metasediments. Note the apophysis to sill. tion. A special session is planned for the The nature of the schedule led me to wonder San Francisco AGU meeting (session V28: whether the two hours flying time and the Magmatic Systems: An Antarctic Perspective). Marsh BA (2004) Magmatic mush column Rosetta multiple landings were more detrimental to Stone: The McMurdo Dry Valleys of Antarctica. the ecosystem than having three extra tents The ESS Contribution number for this paper EOS Transactions AGU 85(47): 497 is: 2005390.

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