HR: 12:05h
AN: PP32A-08    [Abstracts]
TI: Constraining the last glacial maximum and deglaciation of Mauna Kea with cosmogenic surface exposure dating
AU: * Anslow, F S
EM: anslowf@geo.oregonstate.edu
AF: Department of Geosciences, 104 Wilkinson Hall Oregon State University, Corvallis, OR 97331,
AU: Clark, P
EM: clarkp@onid.orst.edu
AF: Department of Geosciences, 104 Wilkinson Hall Oregon State University, Corvallis, OR 97331,
AU: Kurz, M
EM: mkurz@whoi.edu
AF: Woods Hole Oceanographic Institution, Clark 419 MS #25, Woods Hole, MA 02543,
AU: Hostetler, S
EM: steve@coas.oregonstate.edu
AF: United States Geological Survey, 104 Wilkinson hall Oregon State University, Corvallis, OR 97331,
AB: We have sampled glacially deposited boulders on several moraines associated with Pleistocene glacial advances On Mauna Kea, Hawaii. We retrieved ultramafic xenoliths on these boulders and have measured cosmogenic 3He concentrations in olivine and clinopyroxine mineral grains to obtain surface exposure ages. Our two oldest-dated moraines, stratigraphically most distal to the ice cap, yield ages of 21.6 ±1.6 ka BP and 23.8 ±1.7 ka BP. We interpret these ages to indicate the onset of ice cap retreat and the end of the LGM local to Mauna Kea. Samples from a moraine that cross-cuts our older-dated moraine yield a boulder mean age of 14.9 ±1.9 ka BP. This age, combined with a single boulder age near the summit of 16.2 ±1.2 ka BP imply a rapid and complete deglaciation before 13.7 ka BP. Surface exposure ages from striated and well-polished bedrock samples upslope from the Makanaka terminal moraines yield a mean age of 19.6 ± 1.4 ka BP. Assuming that there was no inherited cosmogenic 3He in these, one interpretation of these ages suggests a minimum retreat from the LGM extent of ~1.5 km after 21.6 ka BP followed by a 2 kyr readvance culminating in complete deglaciation by 14.9 ka BP. Our ages are the first to show that deglaciation of Mauna Kea, Hawaii began no later than 20.0 ka BP and that the duration of readvance culminating in final deglaciation could have been as long as 2 kyr.
DE: 0720 Glaciers
DE: 0798 Modeling
DE: 4918 Cosmogenic isotopes (1150)
DE: 4938 Interhemispheric phasing
DE: 9355 Pacific Ocean
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting