Browsing by Author "Kong, P"
Now showing 1 - 9 of 9
Results Per Page
Sort Options
- ItemCosmogenic 10Be inferred lake-level changes in Sumxi Co basin, Western Tibet(Elsevier, 2007-03-01) Kong, P; Na, C; Fink, D; Huang, F; Ding, LMost Tibetan lakes are surrounded by conspicuous regressive shorelines attesting to high-water levels in the past. Concentrations of the in situ produced cosmogenic radionuclide Be-10 in bedrock from the three highest terraces surrounding Sumxi Co, situated in Western Kunlun, indicate that the highest lake-level appeared before 10,000-11,500 yr, and most likely between 11,000 and 12,800 yr. Younger ages for the two lower terraces imply regression of Sumxi Co during the early-mid Holocene. The concurrency of the highest lake-level with orbitally induced maximum northern hemisphere summer insolation suggests that the increase in water supply to Sumxi Co was most likely associated with increased recharge from melting glaciers. We conclude that the enhanced Indian monsoon during the early Holocene did not penetrate the Tibetan plateau and affect the northwestern part of Tibet significantly. © 2006, Elsevier Ltd.
- ItemDip-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, WThe 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.
- ItemErosion in northwest Tibet from in-situ-produced cosmogenic 10Be and 26Al in bedrock(Wiley, 2007-01) Kong, P; Na, C; Fink, D; Ding, L; Huang, FConcentrations of in-situ-produced cosmogenic nuclides 10Be and 26Al 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 (10Be) and erosion rates between 4·0 and 24 mm ka−1. The erosion rates are significantly higher than those in similarly arid 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 arid 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. 5-3 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. Copyright © 2006 John Wiley & Sons, Ltd.
- ItemErosion 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, FXConcentrations 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.
- ItemFluctuation 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, CGCosmogenic 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
- ItemLate miocene ice sheet elevation in the Grove Mountains, East Antarctica, inferred from cosmogenic Ne-21-Be-10-Al-26(Elsevier, 2010-05) Kong, P; Huang, FX; Liu, XH; Fink, D; Ding, L; Lai, QZThe Grove Mountains, lying in the interior of East Antarctica, consist of 64 nunataks. Geomorphic characteristics of the nunataks suggest that past ice sheet elevations have overtopped the summits of the Grove Mountains. Cosmogenic 21Ne, 10Be and 26Al dating yields surface exposure ages of five bedrock samples taken from the crest of Mount Harding, a typical nunatak in the Grove Mountains. Using multi-nuclide fitting, we have calculated the time that the ice sheet retreated below the crest of Mount Harding; all data point to the late Miocene, ~ 6.3 Ma ago. The results provide the first land-based evidence of the elevation of the East Antarctic Ice Sheet in the Grove Mountains in Late Miocene, which reached 2300 m, 200 m higher than the current ice sheet level. The higher than current ice sheet elevations during the late Miocene together with contemporaneously higher temperatures in the Southern Ocean suggest that moisture transport plays an important role in ice sheet expansion in the interior of East Antarctica. © 2010, Elsevier Ltd.
- ItemLate quaternary glaciation of the Tianshan, Central Asia, using cosmogenic Be-10 surface exposure dating(Elsevier, 2009-09) Kong, P; Fink, D; Na, C; Huang, FGlacial deposits are present at the head of the Urumqi River valley, Tianshan, Central Asia. 10Be surface exposure ages of 15 boulders from three sites along a 12 km valley transect range from 9 to 21 ka suggesting emplacement by glacial retreat and advance commencing at the global last glacial maximum (LGM) and most likely abating in the early Holocene. Although the age spread for a given locality is not small, perhaps indicating post-depositional reworking, maximum ages per site are either coeval with or are post-LGM and inconsistent with previous pre-LGM electron spin resonance ages. © 2009, Elsevier Ltd.
- ItemMinimum bedrock exposure ages and their implications: Larsemann Hills and neighboring Bolingen Islands, East Antarctica(Wiley-Blackwell, 2010-06-01) Huang, FX; Li, GW; Liu, XH; Kong, P; Ju, YT; Fink, D; Fang, AM; Yu, LJConsiderable controversy exists over whether or not extensive glaciation occurred during the global Last Glacial Maximum (LGM) in the Larsemann Hills. In this study we use the in situ produced cosmogenic nuclide 10Be (half life 1.51 Ma) to provide minimum exposure ages for six bedrock samples and one erratic boulder in order to determine the last period of deglaciation in the Larsemann Hills and on the neighboring Bolingen Islands. Three bedrock samples taken from Friendship Mountain (the highest peak on the Mirror Peninsula, Larsemann Hills; ∼2 km from the ice sheet) have minimum exposure ages ranging from 40.0 to 44.7 ka. The erratic boulder from Peak 106 (just at the edge of the ice sheet) has a younger minimum exposure age of only 8.8 ka. The minimum exposure ages for two bedrock samples from Blundell Peak (the highest peak on Stornes Peninsula, Larsemann Hills; ∼2 km from the ice sheet) are about 17 and 18 ka. On the Bolingen Islands (southwest to the Larsemann Hills; ∼10 km from the ice sheet), the minimum exposure age for one bedrock sample is similar to that at Friendship Mountain (i.e., 44 ka). Our results indicate that the bedrock exposure in the Larsemann Hills and on the neighboring Bolingen Islands commenced obviously before the global LGM (i.e., 20–22 ka), and the bedrock erosion rates at the Antarctic coast areas may be obviously higher than in the interior land. © 2010, Wiley-Blackwell.
- ItemMoraine dam related to late quaternary glaciation in the Yulong Mountains, southwest China, and impacts on the Jinsha River(Elsevier, 2009-12) Kong, P; Na, C; Fink, D; Zhao, X; Xiao, WThe Yulong Mountain massif is tectonically active during Quaternary and contains the southernmost glacierized mountains in China, and all of Eurasia. Past glacial remnants remain preserved on the east and west sides of the Yulong Mountains. A ridge of moraine protruded into the Jinsha River at the Daju Basin, damming the river, and forming a lake at the head of the Jinsha River. Cosmogenic 10Be and 26Al provide exposure age dates for the moraine-based fluvial terraces left behind after the dam breached, and for moraine boulders on both the eastern and western sides of the Yulong Mountains. Our results yield exposure ages for the terraces that range from 29 ka to 8 ka, and a downcutting rate of 7.6 m/ka. The preservation of the remaining dam for over 10,000 years suggests stability of the moraine dam and gradual erosion of the dam during drainage of the dammed lake. From the relationship between exposure ages and elevations of the fluvial terraces located in different walls of the Daju fault, we obtain a late Quaternary dip-slip rate of about 5.6 m/ka for the Daju fault. The exposure ages of 10.2 ka and 47 ka for moraine boulders located in the east and west sides of the Yulong Mountains, respectively, coincide with warm periods in the late Quaternary. This implies that precipitation provides the major control for glaciations on the Yulong Mountains, a domain of the southwest Asian monsoon. © 2009, Elsevier Ltd.