HR: 0800h
AN: H31A-1271    [Abstracts]
TI: Patterns of Denudation in a Linked Normal Fault Array
AU: * Krugh, W C
EM: william.krugh@erdw.ethz.ch
AF: ETH Zentrum, Institute of Geology, Department of Earth Sciences, Zürich, 8092 Switzerland
AU: Densmore, A
EM: alexander.densmore@erdw.ethz.ch
AF: ETH Zentrum, Institute of Geology, Department of Earth Sciences, Zürich, 8092 Switzerland
AU: Seward, D
EM: diane.seward@erdw.ethz.ch
AF: ETH Zentrum, Institute of Geology, Department of Earth Sciences, Zürich, 8092 Switzerland
AB: The growth of a normal fault array, through fault interaction and linkage, results in spatial and temporal variations in both displacement and displacement rate. Before we can investigate the processes, forcings, and responses involved in landform evolution, we must first consider how this transient fault behavior impacts range-scale patterns of denudation. Geologic mapping and low-temperature thermochronology were used to reveal the range-scale denudation pattern along the southern Wassuk Range of Nevada. Located on the western margin of the Basin and Range, the Wassuk Range is a 130 km long footwall block uplifted along its eastern flank by a segmented normal fault array. The two southernmost fault segments are linked by a left-stepping relay zone with the resulting relay ramp inclined shallowly (~7°) toward the south. A ~3 Ma basalt flow (Gilbert et al., 1968), located within the relay ramp and offset along both the inboard and outboard faults (southern and northern fault segments respectively), provides a measure of fault displacement. At the northern end of the relay ramp, the basalt flow is elevated ~500 m above the basin, while at the southern end, it is elevated <100 m above the basin. This geometric relationship indicates that post 3 Ma displacement decreases southward along the outboard fault. Low-temperature thermochronologic data suggests that denudation follows a similar trend. Apparent apatite fission track ages increase from 13.5 ± 0.9 Ma, north of the relay zone, to 46.1 ± 3.1 Ma south of the relay. This southward increase in cooling ages suggests that denudation decreases toward the southern fault tip. While detectable, the relatively small displacement of the basalt flow suggests that recent displacement and denudation may be too low to fully resolve with the apatite fission track data. Therefore, we are in the process of using (U-Th)/He analysis to examine the low temperature cooling signal of the southern Wassuk Range. Results of this study should place additional constraints on the pattern of range-scale denudation.
DE: 1140 Thermochronology
DE: 1824 Geomorphology: general (1625)
DE: 8175 Tectonics and landscape evolution
SC: Hydrology [H]
MN: Fall Meeting 2005