Antarctic glacial chronology : new constraints from surface exposure dating

• Main Author: Ackert, Robert P.
• Format: Thesis
• Language: English
• Published: Massachusetts Institute of Technology and Woods Hole Oceanographic Institution 2000
• Subjects: Glaciers; Antarctic; Patagonia; West Antarctic Ice Sheet; McMurdo Sound; East Antarctic Ice Sheet; Transantarctic Mountains; Byrd; Marie Byrd Land; Beardmore; Beardmore Glacier; Dromedary; Dominion Range; Koettlitz Glacier; Mount Waesche; Antarc*; Antarctica; Ice Sheet
• Online Access: https://hdl.handle.net/1912/4123

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2000 Surface exposure dating, using the concentration of cosmogenic nuclides (3He, 21Ne, and 36Cl) in moraine boulders, combined with mapping of glacial moraines from three key locations, is used to provide new constraints to Antarctic glacial chronology. The results are used to reconstruct past West Antarctic Ice Sheet (WAIS) geometry and test models of WAIS behavior. Mount Waesche is a volcanic nunatak near the dome of the WAIS in Marie Byrd Land. The Dominion Range is at the head of the Beardmore Glacier, an outlet glacier of the East Antarctic Ice Sheet in the Transantarctic Mountains. Dromedary Platform is a bench along the Koettlitz Glacier which flows into southern McMurdo Sound. In addition, a new 3He production rate calibration, and determination of initial 3He/4He in Ferrar Dolerite and Beacon Sandstone, substantially reduce uncertainties in Antarctic exposure ages. 3He production rates of 129 ± 4 atoms/g/yr (olivine) and 124 ± 4 atoms/g/yr (clinopyroxene) at sea level, high latitude, are determined from an independently dated 125 ka lava flow in Patagonia (46°S). Paired 3He and 36Cl measurements are consistent with negligible surface erosion which is inferred from flow morphology. These mid-latitude, long term, 3He production rates reduce uncertainties previously introduced when scaling production rates calibrated at lower latitudes to Antarctica. The results also confirm the compositional dependence of 3He production rates predicted by theoretical calculations and are used to scale the production rates to quartz. Determinations of initial 3He/4He in pyroxene from shielded dolerite and by incremental heating of quartz show that inherited (nucleogenic) 3He concentrations are very low (3He/4He <.010 R/Ra). For exposures longer than about 30,000 years the inherited component can be ignored. These results enable ...