(Denton et al., 1991 ; Ing lfsson et al., 1998 ; Anderson, 1999 ;Denton et al.,1984), (Dowsett et al.,1996)

Transcription

1 16 1 Vol. 16, No CHIN ESE JOURNAL OF POLAR RESEARCH March 2004 (, ) (, ) (, ) 10 Be 26 Al, 2Ma, (L GM), 200m,, (L GM), 10 Be 26 Al km 3, 83 %, 60 (Denton,2002),,, (Denton et al., 1991 ; Ing lfsson et al., 1998 ; Anderson, 1999 ;Denton et al.,1984),, (Dowsett et al.,1996) [ ] , [ ] (2001DIA50040) [ ],,1974,

2 1 : 23,, (Clapperton Dugden,1991 ; Warnke et al.,1996 ; Sugen et al.,1995), 1/ 3 ( Webb Harwood,1990 ; Wilson, 1995) (Lal,1991 ;Nishiizumi et al.,1991 ; Ivy2Ochs et al.,1995 ; Sch afer et al.,1999 ;,1997 ;,1999) 10 Be 26 Al ( Grove Mountains) (Zakharoff Ridge) (Mount Harding),, 440km, S, E 64 (Liu et al., 2003), 3200km 2, m, m,, (Denton Hughs,2002 ; Huybrechts,2002) , (Liu et al.,2003 ;Li et al.,2003 ;,2003),, 100m,, 120m 10 Be 26 Al, 2 (Zakharoff Ridge) (Mount Harding) ( ) ( 1), 2250m, 150m, 2300m, 200m, (,2002 ;Liu et al.,2003), 4, 30 %, cm R8201,R8205, 2230m,R , 20m 1

3 Fig. 1. Map of the Grove Mountains showing sample locations, mm,, 1 % HF 1 % HNO 3 4 5,, 0. 5mg 9 Be Be Al, 850 C ( Kohl Nishiizumi,1992) 10 Be 26 Al (Australian Nuclear Science & Technology Orgnisation, ANSTO) (AMS) Al ( ICP2AES), Al 10 2 ppm ( 1),, 1 % 10 Be/ 9 Be , 3 10 Be 26 Al : N = P ( + / ) - ( + [1 - e / ) T ] + N 0 e - T (1) N ( / ), P ( / ), T ( ), ( / ),, ( / ), ( / ) N 0, 0 (Nishiizumi et al.,1991 ;Lal,1991), 0 10 Be 26 Al

4 1 : 25, 10 Be 26 Al Stone (2000), 10 Be 26 Al 5. 1 / / Stone (2000), 200m, Stone (2000) Dunai (2000), Lal (1991) Stone (2000) 1 1 Table 1. Altitudes and minimum exposure ages of the bedrock samples in the Grove Mountains Al 10Be/ 9 Be 26Al/ Al (m) ( 10-6 ) a (g) (10-12 ) ( %) (10-12 ) ( %) 10Be (10 6 / ) 26Al (10 6 / ) 26Al/ 10 Be 10Be (Ma) 26Al (Ma) R / / R / R / / R / R / b / : 10 Be 26 Al ( 10 %, Gosse et al.,2001). aicp2aes 5 %. b Ma R9201 ( 200m) 10 Be 26 Al ( ) Ma ( / ) Ma,, R Be 26 Al ( / ) Ma ( / ) Ma, R9201 R Be, 10 Be 26 Al, 10 Be 26 Al, 10 Be 10 Be/ 26 Al 10 Be 2, R8201, R8203,R8205 R9201,,, R9207, 10 Be, R9201,,,

5 26 16, R9201 (2300m), 200m, (L GM),L GM (Bentley,1999), 10 2 m (Jouzel,1989),, 200m, L GM R m,, LM G, 2 26 Al/ 10 Be 10 Be 10 Be Fig. 2. Plot of 26 Al/ 10 Be vs. 10 Be concentrations. 10 Be concentrations have been normalized to sea level, high latitude of northern hemisphere 1 0,, Nishiizumi et al. (1991) cm/ Ma Ivy2Ochsd et al. (1995) 5cm/ Ma Lal (1991) Stone Ivy2Ochsd 5cm/ Ma, 5cm/ Ma R9201 R Be, ( / ) Ma ( / ) Ma,,, (Joseph et al.,2002 ;Crowley,1991) 5 10 Be 26 Al

6 1 : 27, 2. 3Ma ( ), 200m,,,,,Lal D (1997) : 10 Be 26 Al,,3, ,, (1999) :,,,, ( ),,, ,, (2003) :,,23,35 39,, (2002) :,,18,91 99 Anderson JB (1999) : Antarctic Marine Geology, Cambridge University Press, Cambridge, Bentley MJ (1999) : Volume of Antarctic ice at the last glacial maximum, and its impact on global sea level change, Quater2 nary Science Reviews, 18, Clapperton CM, Dugden DE (1991) : Late Cenozoic glacial history of the Ross Embayment, Antarctic, Quaternary Science Reviews, 9, Crowley TJ (1991) : Modeling Pliocene warmth, Quaternary Science Reviews, 10, Denton GH, Hughs TJ (2002) : Reconstructing the Antarctic ice sheet at the last glacial maximum, Quaternary Science Re2 views, 21, Denton GH, Prentice ML, Burkle L H (1991) : Cenozoic history of the Antarctic ice sheet, In : The Geolgoy of Antarctica, Ed. by Tingey RJ, Clarendon Press, Oxford, Denton GH, Prentice ML, Kellogg DE et al. (1984) : Late Tertiary history of the Antarctic ice sheet : Evidence from the Dry Valleys, Geology, 12, Dowsett HJ, Barron JA, Poore RZ (1996) : Middle Pliocene sea surface temperatures : A global reconstruction, Marine Mi2 cropaleontology, 27, Dunai TJ (2000) : Scaling factors for production rates of in situ produced cosmogenic nuclides : A critical revaluation, Earth and Planetary Science Letters, 176, Gosse J C, Phillips FM (2001) : Terrestrial in situ cosmogenic nuclides : theory and application, Quaternary Science Re2 views, 20, Huybrechts P (2002) : Sea2level changes at the L GM from ice2dynamic reconstructions of the Greenland and Antarctic ice sheet during the glacial cycles, Quaternary Science Reviews, 21, Ing lfsson, Hjort C, Berkman PA et al. (1998) : Antarctic glacial history since the Last Glacial Maximum : an overview of the record on land, A ntarctic Science, 10, Ivy2Ochs S, Schl chter C, Kubik PW et al. (1995) : Minimum 10 Be exposure ages of early Pliocene for the Table Mountain plateau and the Sirius Group at Mount Fleming, Dry Valleys, Antartica, Geology, 23 (11), Joseph L H, Rea D K, van der Pluijm BA et al. (2002) : Antarctic environmental variability since late Miocene : ODP Site 745, the East Kergulen sediment drift, Earth A nd Planetary Science Letters, 201, Jouzel J, Raisbeck G, Benoist J P et al. (1989) : A comparison of deep Antarctic ice cores and their implications for climate between 65,000 and 15,000 years ago, Quaternary Research, 31, Kohl CP, Nishiizumi K ( 1992) : Chemical isolation of quartz for measurement of in2situ2produced cosmogenic nuclides, Geochi mical et Cosmochi mica Acta, 56, Lal D (1991) : Cosmic ray labeling of erosion : in situ nuclide production rates and erosion models, Earth and Planetary Sci2 ence Letters, 104, Li X, Liu X, J u Y et al. (2003) : Properties of soils in Grove Mountains, East Antarctica, Science in China (Series D), 46,

7 28 16 Liu X, Zhao Y, Liu X et al. (2003) : Geology of the Grove Mountains in East Antarctic, Science in China (Series D), v. 46, Miller MF, Mabin MCG (1998) : Antarctic Neogene landscape in the refrigerator or in the deep freeze? GSA Today, 8, 1 3. Nishiizumi K, Kohl CP, Arnold J R et al. (1991) : Cosmic ray produced 10 Be and 26 Al in Antarctic rocks : exposure and ero2 sion history, Earth and Planetary Science Letters, 104, Sch afer J M, Ivy2Ochs S, Wieler R et al. (1999) : Cosmogenic noble gas studied in the oldest landscape on earth : surface exposure ages of the Dry valleys, Antarctica, Earth and Planetary Science Letters, 167, Stone JO (2000) : Air pressure and cosmogenic isotope production, Journal of Geophysical Research, 105, 23,753 23, 759. Sugen DW, Marchant DR., Potter N et al. (1995) : Preservation of Miocene glacier ice in the East Antarctic, Nature, 376, Warnke DA, Marzo B, Hodell DA (1996) : Major deglaciation of east Antarctic during the early Pliocene? Not Likely from marine perspective, M arine Micropaleontology, 27, Webb PN, Harwood DM, Dugden DE (1990) : Late Cenozoic glacial history of the Ross Embayment, Antarctic, Quater2 nary Science Reviews, 10, Wilson GS (1995) : The Neogene east Antarctic ice sheet : A dynamic or stable feature? Quaternary Science Reviews, 14, BEDROCK EXPO SURE A GES IN THE GROVE MOUNTAINS, INTERIOR EAST ANTARCTICA Huang Feixin (Laboratory of Lithosphere Tectonic Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing , China) Liu Xiaohan ( Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing , China) Kong Ping, J u Yitai, Fang Aimin, Li Xiaoli, Na Chunguang ( Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing , China) Abstract Exposure ages of bedrock samples taken f rom two nunataks in t he Grove Mountains ( GMs), interior East Antarctica, are studied by dating i n sit u produced cosmogenic 10 Be and 26 Al. The results indicate that the minimum exposure time of the five samples are all about 2Ma, much older than that of Last Glacial Maximum. This as well as the field obser2 vations indicates that the thickness of the interior East Antarctic Ice Sheet ( EAIS) had re2 duced more than 200m since early to middle Pliocene. From then on, even in the period of the Last Glacial Maximum (L GM), the elevation of the interior EAIS is never higher than that of early to middle Pliocene Key words east Antarctic ice sheet, Grove Mountains, Pliocene, 10 Be and 26 Al, exposure ages, deglaciation.