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Differential Movement Across Byrd Glacier, Antarctica, As Indicated by Apatite

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Differential Movement Across Byrd Glacier, Antarctica, As Indicated by Apatite 1 Differential Movement across Byrd Glacier, Antarctica, 2 3 as indicated by Apatite (U–Th)/He thermochronology 4 Q1 and geomorphological analysis 5 6 7 Q2 D. J. FOLEY, E. STUMP, M. VAN SOEST, K. X. WHIPPLE & K. V. HODGES 8 School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA 9 10 11 Abstract: The objectives of this study were to assess possible differential movement across an 12 inferred fault beneath Byrd Glacier, and to measure the timing of unroofing in this portion of 13 the Transantarctic Mountains. Apatites separated from rock samples collected from known 14 elevations at various locations north and south of Byrd Glacier were dated using single crystal (U–Th)/He analysis. Results indicate a denudation rate of c. 0.04 mm a21 in the time range c. 15 140–40 Ma. Distinct age v. elevation plots from north and south of Byrd Glacier indicate an 16 offset of c. 1 km across the glacier with south side up. A Landsat image of the Byrd Glacier 17 area was overlain on an Aster Global Digital Elevation Model and spot elevations of the Kukri 18 erosion surface to the north and south of Byrd Glacier were mapped. The difference in elevation 19 of the erosion surface across Byrd Glacier also shows an offset of c. 1 km with south side up. 20 Results support a model of relatively uniform cooling and unroofing of the region with later, 21 post-40 Ma fault displacement that uplifted the south side of Byrd Glacier relative to the north. 22 23 Supplementary material: Apatite (U–Th)/He data is available at http://www.geolsoc.org.uk/ Q3 SUP00000 24 25 26 27 28 Byrd Glacier, one of the major outlet glaciers cross- of samples collected from ‘vertical profiles’ 29 ing the Transantarctic Mountains (Fig. 1), marks a (Gleadow & Fitzgerald 1987; Fitzgerald & Glea- 30 major discontinuity in the Neoproterozoic–early dow 1988; Fitzgerald 1992; Fitzgerald & Stump 31 Palaeozoic Ross orogen, with plutonics and upper 1997; Lisker 2002). The Transantarctic Mountains 32 amphibolite-grade metamorphics to the north and are ideally suited for such studies because mag- 33 lower greenschist-grade metamorphics and lime- matism throughout the entirety of the range occur- 34 stones to the south, indicating considerable differen- red in a brief period during the Jurassic (Fleming 35 tial unroofing of the orogen prior to deposition of et al. 1997), totally annealing older fission tracks, 36 the Beacon Supergroup on the Kukri erosion sur- except at two known localities where Palaeozoic 37 face (Stump et al. 2005). Grindley & Laird (1969) apatite fission track ages survive (the western, 38 mapped post-Beacon faults beneath Byrd Glacier inland margin of northern Victoria Land (Fitzge- 39 and other outlet glaciers in the region, but cited no rald & Gleadow 1988) and the Miller Range at the 40 evidence other than the presence of the glaciers inland margin of the central Transantarctic Moun- 41 themselves. tains (Fitzgerald 1994)). When data are plotted 42 This study asked the question, whether there on age v. elevation diagrams, they indicate that 43 indications of displacement across the inferred exhumation of the entire Transantarctic Mountains 44 Byrd fault, and if yes, what the amount of throw began in the Early Cenozoic, ranging between 45 45 was. To assess possible differential movement and 55 Ma depending on the region. The central 46 across Byrd Glacier, we have used a two-pronged Transantarctic Mountains and the Scott Glacier 47 approach combining thermochronology, (U–Th)/ area also have indications of pulses of exhumation 48 He analysis of apatite and geomorphology, compar- in the Cretaceous (Stump & Fitzgerald 1992; Fitz- 49 ing elevations of the Kukri erosion surface on the gerald 1994). 50 north and south sides of Byrd Glacier. One study utilizing (U–Th)/He analysis was 51 conducted in the Ferrar Glacier area of southern 52 Victoria Land where vertical profiles have been ana- 53 Background lysed on opposite sides of the glacier (Fitzgerald 54 et al. 2006). Although the data are very scattered, 55 Our understanding of the history of uplift and probably because of a variety of complications 56 denudation of the Transantarctic Mountains is associated with the technique, in general they indi- 57 based primarily on low-temperature thermochrono- cate slow cooling in the Late Cretaceous and an 58 logical studies using apatite fission track analysis increased cooling rate in the early Cenozoic. From:Hambrey, M. J., Barker, P. F., Barrett, P. J., Bowman, V., Davies, B., Smellie,J.L.&Tranter, M. (eds) Antarctic Palaeoenvironments and Earth-Surface Processes. Geological Society, London, Special Publications, 381, http://dx.doi.org/10.1144/SP381.25 # The Geological Society of London 2013. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics.
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