T160 Quantifying Geomorphic Processes and Rates of Landscape Evolution (Posters)

Monday, 23 October 2017
9:00 AM - 6:30 PM
Halls 4EF

CONSISTENT SLOW EXHUMATION IN A LATE CENOZOIC GLACIATED LANDSCAPE, THE PRESIDENTIAL AND CARTER RANGES OF THE WHITE MOUNTAINS IN NEW HAMPSHIRE, USA

Paper number: T160-16
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

A comparison of denudation rates averaged over a 106-7 yr timescale using apatite (U-Th)/He thermochronology and averaged over a 103-4 yr timescale using the in situ terrestrial cosmogenic nuclide (TCN) 10Be methods allows an examination of the effect of late-Cenozoic glaciation on denuding the Presidential and Carter Ranges of the White Mountains, New Hampshire, USA. Thermal modeling of apatite (U-Th)/He ages from Mt. Washington in the Presidential Range (n=4, 91.7 to 117.3 Ma) indicate that beginning in the Late Cretaceous exhumation rates slowed from ~0.03 to ~0.01 mm yr-1 in valleys and stagnated over ridges. This resulted in ~1 km of relief production after ~100 Ma, or between 100 - 60 Ma if the data in this study are resolved with previous apatite fission track work (Roden-Tice et al. 2012). Summit bedrock and talus 10Be concentrations and exposure ages from the Presidential and Carter Ranges (n=8; ~14–190 × 104 atoms g-1 SiO2; 14–130 ka) indicate inheritance of 10Be prior to the last glacial maximum resulting from cold-based ice cover, in agreement with previous work in the region (Bierman et al., 2015). The 10Be concentrations in till samples across the field area (n=5; ~2–7 × 104 atoms g-1 SiO2) are greater than can be ascribed to production since deposition. This implies inheritance across the study area, not just on summits, suggesting that that cold based-ice and limited magnitudes of glacial erosion also affected lower elevation portions of the landscape. Be-10 concentrations from catchment-wide sand and modern flood deposits (n=14; 5–19 × 104 atoms g-1 SiO2) are statistically the same as those from till, higher than those from colluvium (n=2; 2–7 × 104 atoms g-1 SiO2), and lower than those from bedrock and talus. These 10Be concentrations suggest that the post-glacial sediment budget is dominantly derived from remobilized glacial sediment. As such, late Cenozoic glaciation did modify existing topography but it did not significantly produce relief or accelerate exhumation in Presidential and Carter Ranges of New Hampshire.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-304036

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