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McDannell, K.T., 2011

Exhumation in the Bendeleben Mountains (Seward Peninsula, Alaska) constrained by (U-Th)/He thermochronology

Bibliographic Reference

McDannell, K.T., 2011, Exhumation in the Bendeleben Mountains (Seward Peninsula, Alaska) constrained by (U-Th)/He thermochronology: Morgantown, West Virginia, West Virginia University, M.S. thesis, viii, 46 p., (some color) illust., (some color) maps.


In the Bendeleben Mountains of the Seward Peninsula, mid-Cretaceous granite batholiths and high-grade metamorphic rocks are exposed on the footwall of a major uplifted block bounded by the recently active E-W-striking Bendeleben normal fault. The Bendeleben fault can be mapped through well preserved normal fault scarps 4-7 m in height along the southern flank of the mountains. Quaternary basalt flows that are likely associated with this extensional deformation occur in the Imuruk volcanic field located 10-20 km north of the Bendelebens and as smaller basaltic fields in the eastern Bendelebens. Current seismic activity, young normal faulting, and Quaternary volcanics all support active extension. South of the Bendeleben fault, there is a broad, low-lying area known as McCarthy's Marsh, which is underlain by basin fill and presumably greenschist facies Nome Group equivalent basement rocks. The Bouguer gravity field shows a negative anomaly of -60 mgals in the basin. Gravity modeling suggests a depth of 3-4 km of sedimentary fill. This study is focused on constraining the magnitude of exhumation in the Bendelebens using apatite helium thermochronology. Measured helium ages from the footwall block suggest exhumation occurred mainly in the Eocene, with a weighted mean age of 38.7 +/- 2.4 Ma for 15 samples. Pecube and HeFTy time-temperature modeling illustrate that episodic exhumation of the Bendelebens occurred since the Cretaceous, with a major event in the Eocene, and activity slowing in Oligocene-Miocene time. A poor age-elevation relationship between samples and lack of age correlation with distance from the fault suggest minimal block rotation and a steeply dipping, long-lived normal fault. Timing of extension in the Seward Peninsula can be correlated with offshore extension in the Hope basin to the NW and suggests that these extensional systems are linked and document regional deformation across the Bering region. The regional tectonic model proposed in previous studies suggests lateral and clockwise-rotational extrusion of an independent Bering block toward eastern Russia that causes the dominant mode of extensional deformation in the Seward Peninsula.

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