Persistent long-term (
            <i>c.</i>
            24 Ma) exhumation in the Eastern Alaska Range constrained by stacked thermochronology

Benowitz, Jeff; Layer, Paul W.; VanLaningham, Sam

doi:10.1144/sp378.12

Cited by 61 publications

(102 citation statements)

References 78 publications

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“…Within each transect, samples from Greater Himalayan rocks were collected at similar elevations (Table 1). We obtained multi-grain aliquot 40 (Benowitz et al 2013) and muscovite from the other samples was dated at the New Mexico Geochronology Research Laboratory (Sanders et al 2006). Argon isotopic data are presented in Table 2.…”

Section: Methodsmentioning

confidence: 99%

Muscovite ⁴⁰ Ar/ ³⁹ Ar ages help reveal the Neogene tectonic evolution of the southern Annapurna Range, central Nepal

Martin

Copeland

Benowitz

2014

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We present new muscovite 40 Ar/ 39 Ar ages from thirteen Greater Himalayan rocks and one Lesser Himalayan rock collected from four north-trending transects across the southern Annapurna Range. Combining the new data with previously published ages leads to the following new insight into the tectonic development of the southern Annapurna. Muscovite cooling ages from Greater Himalayan rocks are c. 16-10 Ma in the western Annapurna and c. 6-2 Ma in the eastern Annapurna, revealing a decrease of 4 -14 Ma from west to east. Similarly, the muscovite cooling age from one Lesser Himalayan rock in the west is c. 7 Ma and ages from several samples in the east are c. 5-2 Ma, indicating a decline of 2-5 Ma towards the east. Earlier cooling in the western Annapurna can be explained by along-strike differences in the geometry of the frontal ramp on the underlying thrust that carries these Greater and Lesser Himalayan rocks and/or by a NE-striking fault that cut these rocks. In Greater Himalayan rocks from the Modi river valley, one sample yielded muscovite 40 Ar/ 39 Ar ages of 18.0 + 0.7 and 16.2 + 0.5 Ma for grain sizes of approximately 750 and 200 mm, respectively. In contrast, a sample collected 200 m structurally lower produced ages of 12.6 + 0.2 and 9.9 + 0.1 Ma for these two grain sizes. The northdipping Bhanuwa fault has been proposed between these samples, with different authors arguing for normal or thrust-sense motion. Our newfound pattern of an older muscovite 40 Ar/ 39 Ar age pair in the hanging wall supports arguments for the existence of the Bhanuwa fault and suggests normal sense motion.Supplementary material: Analytical methods, thin section observations, data tables, and plots of argon data for each sample are available at

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Section: Methodsmentioning

confidence: 99%

Muscovite ⁴⁰ Ar/ ³⁹ Ar ages help reveal the Neogene tectonic evolution of the southern Annapurna Range, central Nepal

Martin

Copeland

Benowitz

2014

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“…In general, the regions of high topography in the Alaska Range (glaciated regions on Fig. 3) are associated with younger cooling ages, whereas areas of lower average topography have low -temperature cooling ages that reflect plu-ton cooling and not exhumation-related cooling (Fitzgerald et al, 1995;Benowitz et al, 2011Benowitz et al, , 2013. Exhumation in the Alaska Range is neither synchronous nor evenly distributed about the arc of the Denali fault, suggesting that the rock uplift is primarily controlled by local structures rather than far-field processes.…”

Section: Quaternary Faults Of the Alaska Rangementioning

confidence: 99%

Slip partitioning along a continuously curved fault: Quaternary geologic controls on Denali fault system slip partitioning, growth of the Alaska Range, and the tectonics of south-central Alaska

2015

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Active transpressional fault systems are typically associated with the development of broad zones of deformation and topographic development; however, the complex geometries typically associated with these systems often make it difficult to isolate the important boundary conditions that control transpressional orogenic growth. The Denali fault system is widely recognized as transpressional due to the presence of the Denali fault, a major, active, right-lateral fault, and subparallel zones of thrust faults and fault-related folding along both the north and south flanks of the Alaska Range. Measured Quaternary and Holocene slip rates exist for the Denali fault system and portions of the adjacent thrust system, but the partitioning of fault slip between contractional and translational components of this transpressional system has not been previously studied in detail. Exploiting the relatively simple geometry of the Denali fault, we analyze the style and distribution of active faulting within the Alaska Range to define patterns of strain accommodation and determine how contractional and translational strain is partitioned across the Denali fault system. As the trace of the Denali fault curves by ~70° across central Alaska, the mean strike of the thrust system to the north remains subparallel to the Denali fault, while to the south, the few faults with known or suspected Quaternary offset are oblique to the Denali fault. This relationship suggests that as the Denali fault system accommodates local fault-parallel strike slip, it partitions the residual part of the regional NW-directed plate motion into NW-SE shortening south of the Denali fault and shortening perpendicular to the Denali fault to the north. The degree of slip partitioning is consistent with a balanced slip budget for the two primary faults that contribute displacement to the Denali fault system (the eastern Denali fault and Totschunda fault). The current obliquity of displacement south of the Denali fault is the result of the late Cenozoic development of the Totschunda fault, which provides a more direct connection for the transfer of strain from the Fairweather transform fault to the Denali fault system. The transmitted strain is partitioned into right-lateral slip on the Denali fault and into Denali fault-normal shortening that is accommodated by thrust faulting in the Alaska Range and distributed left-lateral slip faulting within interior Alaska to the north.

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“…Numerous studies using lowtemperature thermochronology have focused on exhumational patterns across major fault systems associated with fl at-slab subduction in southern Alaska, including studies in the Alaska Range (e.g., Fitzgerald et al, 1995;Haeussler et al, 2008Haeussler et al, , 2011Benowitz et al, 2011Benowitz et al, , 2012Benowitz et al, , 2013, Chugach Mountains (Little and Naeser , 1989;Buscher et al, 2008;Arkle et al, 2013), and Saint Elias Mountains (e.g., Berger et al, 2008aBerger et al, , 2008bBerger and Spotila, 2008;Meigs et al, 2008;Enkelmann et al, 2008Enkelmann et al, , 2009Spotila and Berger, 2010). Some of these studies detected loci of rapid exhumation, particularly in the Saint Elias and western Chugach Mountains, which may be the result of crustalscale lithologic backstops to upper crustal rock deformation above the subducting Yakutat microplate.…”

Section: Introductionmentioning

confidence: 99%

Focused rock uplift above the subduction décollement at Montague and Hinchinbrook Islands, Prince William Sound, Alaska

et al. 2015

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Megathrust splay fault systems in accretionary prisms have been identifi ed as conduits for long-term plate motion and signifi cant coseismic slip during subduction earthquakes. These fault systems are important because of their role in generating tsunamis, but rarely are emergent above sea level where their long-term (million year) history can be studied. We present 32 apatite (U-Th)/He (AHe) and 27 apatite fi ssion-track (AFT) ages from rocks along an emergent megathrust splay fault system in the Prince William Sound region of Alaska above the shallowly subducting Yakutat microplate. The data show focused exhumation along the Patton Bay megathrust splay fault system since 3-2 Ma. Most AHe ages are younger than 5 Ma; some are as young as 1.1 Ma. AHe ages are youngest at the southwest end of Montague Island, where maximum fault displacement occurred on the Hanning Bay and Patton Bay faults and the highest shoreline uplift occurred during the 1964 earthquake. AFT ages range from ca. 20 to 5 Ma. Age changes across the Montague Strait fault, north of Montague Island, suggest that this fault may be a major structural boundary that acts as backstop to deformation and may be the westward mechanical continuation of the Bagley fault system backstop in the Saint Elias orogen. The regional pattern of ages and corresponding cooling and exhumation rates indicate that the Montague and Hinchinbrook Island splay faults, though separated by only a few kilometers, accommodate kilometer-scale exhumation above a shallowly subducting plate at million year time scales. This long-term pattern of exhumation also refl ects short-term seismogenic uplift patterns formed during the 1964 earthquake. The increase in rock uplift and exhumation rate ca. 3-2 Ma is coincident with increased glacial erosion that, in combination with the fault-bounded, narrow width of the islands, has limited topographic development. Increased exhumation starting ca. 3-2 Ma is interpreted to be due to rock uplift caused by increased underplating of sediments derived from the Saint Elias orogen, which was being rapidly eroded at that time.

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Persistent long-term ( c. 24 Ma) exhumation in the Eastern Alaska Range constrained by stacked thermochronology

Cited by 61 publications

References 78 publications

Muscovite ⁴⁰ Ar/ ³⁹ Ar ages help reveal the Neogene tectonic evolution of the southern Annapurna Range, central Nepal

Muscovite ⁴⁰ Ar/ ³⁹ Ar ages help reveal the Neogene tectonic evolution of the southern Annapurna Range, central Nepal

Slip partitioning along a continuously curved fault: Quaternary geologic controls on Denali fault system slip partitioning, growth of the Alaska Range, and the tectonics of south-central Alaska

Focused rock uplift above the subduction décollement at Montague and Hinchinbrook Islands, Prince William Sound, Alaska

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Persistent long-term ( c. 24 Ma) exhumation in the Eastern Alaska Range constrained by stacked thermochronology

Cited by 61 publications

References 78 publications

Muscovite 40 Ar/ 39 Ar ages help reveal the Neogene tectonic evolution of the southern Annapurna Range, central Nepal

Muscovite 40 Ar/ 39 Ar ages help reveal the Neogene tectonic evolution of the southern Annapurna Range, central Nepal

Slip partitioning along a continuously curved fault: Quaternary geologic controls on Denali fault system slip partitioning, growth of the Alaska Range, and the tectonics of south-central Alaska

Focused rock uplift above the subduction décollement at Montague and Hinchinbrook Islands, Prince William Sound, Alaska

Contact Info

Product

Resources

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Muscovite ⁴⁰ Ar/ ³⁹ Ar ages help reveal the Neogene tectonic evolution of the southern Annapurna Range, central Nepal

Muscovite ⁴⁰ Ar/ ³⁹ Ar ages help reveal the Neogene tectonic evolution of the southern Annapurna Range, central Nepal