Browsing by Author "Na, CG"

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    Dip-slip rate determined by cosmogenic surface dating on a Holocene scarp of the Daju fault, Yunnan, China
    (Elsevier, 2010-10-08) Kong, P; Fink, D; Na, CG; Xiao, W
    The Daju and Lijiang-Daju fault zones which bound the Yulong Mountains on its northern and eastern perimeters, respectively, are segments of a continuous fault system that bends at Daju. Uplift of the Yulong Mountains, the southernmost glacierized mountain range in Eurasia, resulted from the normal faulting characteristics of the fault system. Using cosmogenic surface exposure dating with 10Be and 26Al, we have measured bedrock exposure ages as a function of elevation along an exposed bedrock scarp of the Daju fault. 10Be and 26Al exposure ages increase monotonically with elevation ranging from 2.6 to 9.6 ka over the 51 m scarp length giving an average dip-slip rate of 7.5 m/ka during the Holocene period and a vertical uplift rate of 5.7 m/ka. The 5.7 m/ka Holocene uplift rate and supporting geomorphic features suggest that the uplift of the Yulong Mountains mainly occurred in the Quaternary. The fast slip rate and seismic quiescence for the recent 2.8 ka call attention to the possible recurrence of large magnitude earthquake events along the fault zone. © 2010, Elsevier Ltd.
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    Erosion in northwest Tibet from in-situ-produced cosmogenic Be-10 and Al-26 in bedrock
    (John Wiley & Sons, 2007-01) Kong, P; Na, CG; Fink, D; Ding, L; Huang, FX
    Concentrations of in-situ-produced cosmogenic nuclides Be-10 and Al-26 in quartz were measured by accelerator mass spectrometry for bedrock basalts and sandstones located in northwest Tibet. The effective exposure ages range between 23 and 134 ka (Be-10) and erosion rates between 4.0 and 24 mm ka(-1). The erosion rates are significantly higher than those in similarly and Antarctica and Australia, ranging between 0.1 and 1 mm ka(-1), suggesting that precipitation is not the major control of erosion of landforms. Comparison of erosion rates in and regions with contrasting tectonic activities suggests that tectonic activity plays a more important role in controlling long-term erosion rates. The obtained erosion rates are, however, significantly lower than the denudation rate of 3000-6000 mm ka(-1) beginning at c. 53 Ma in the nearby Godwin Austen (K2) determined by apatite fission-track thermochronology. It appears that the difference in erosion rates within different time intervals is indicative of increased tectonic activity at c. 5-3 Ma in northwest Tibet. We explain the low erosion rates determined in this study as reflecting reduced tectonic activity in the last million years. A model of localized thinning of the mantle beneath northwest Tibet may account for the sudden increased tectonic activity at c. 5-3 Ma and the later decrease. © 2006, John Wiley & Sons Ltd.
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    Fluctuation history of the interior East Antarctic ice sheet since mid-pliocene
    (Cambridge University Press, 2008-04) Huang, FX; Liu, XH; Kong, P; Fink, D; Ju, YT; Fang, AM; Yu, LJ; Li, XL; Na, CG
    Cosmogenic Be-10 and Al-26 measurements from bedrock exposures in East Antarctica provide indications of how long the rock surface has been free from glacial cover. Samples from the crests of Zakharoff Ridge and Mount Harding, two typical nunataks in the Grove Mountains, show minimum Be-10 ages of 2.00 +/- 0.22 and 2.30 +/- 0.26 Ma, respectively. These ages suggest that the crests were above the ice sheet at least since the Plio -Pleistocene boundary. Adopting a 'reasonable' erosion rate of 5-10 cm Ma(-1) increases the exposure ages of these two samples to extend into the mid-Pliocene. The bedrock exposure ages steadily decrease with decreasing elevation on the two nunataks, which indicates similar to 200 m decrease of the ice sheet in the Grove Mountains since mid-Pliocene time. Seven higher elevation samples exhibit a simple exposure history, which indicates that the ice sheet in the Grove Mountains decreased only similar to 100 in over a period as long as 1-2 Ma. This suggests that the East Antarctic Ice Sheet (EAIS) was relatively stable during the Pliocene warm interval. Five lower elevation samples suggest a complex exposure history, and indicate that the maximum subsequent increase of the EAIS was only 100 in higher than the present ice surface. Considering the uncertainties, their total initial exposure and subsequent burial time could be later than mid-Pliocene, which may not conflict with the stable mid-Pliocene scenario. © 2008, Cambridge University Press