帕米尔高原冰川流域碎屑颗粒的铀同位素组成及其对沉积物搬运的指示
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摘要
铀(U)同位素作为一种新的地球化学示踪手段,被逐渐用于研究陆地和海洋沉积物的搬运过程。然而,这一新技术能否有效指示不同环境中各类沉积物的搬运还需更多流域数据的支持。本文选取位于帕米尔高原东北部具有显著海拔梯度和气候差异的盖孜河冰川流域作为研究对象,通过该流域河流沉积物细颗粒中的U同位素的活度比((~(234)U/~(238)U)_(AR))的空间变化,探索U同位素指示内陆冰川流域沉积物搬运的可行性。流域内河流沉积物的矿物组成以石英和长石(占51%—77%)为主,表明较弱的风化作用。流域内受冰川侵蚀控制的上游山区支流康西瓦河和木吉河沉积物的(~(234)U/~(238)U)_(AR)范围分别是0.990—1.017和0.988—1.009,盖孜河中下游段河流沉积物的(~(234)U/~(238)U)_(AR)则为0.913—0.997。从上游山区至中下游段显示了一个明显的下降趋势,指示了沉积物搬运过程中(~(234)U/~(238)U)_(AR)的确发生了系统的变化。然而,盖孜河流域碎屑颗粒比表面积和分形维数计算得到的反冲损失参数太低,未能利用U同位素破碎年龄模型获得合理的沉积物搬运时间,该模型如何用到冰川流域尚需更多的研究工作。
Background, aim, and scope The uranium(U)-series isotopes are recently used in the study of the transport processes of terrestrial and marine sediments as one of new geochemical approaches. However, how to use this new approach effectively to trace sediment transport processes still needs more supporting data from various geological and climatic settings. In this study, we analyzed mineralogy and U-series isotopes of fine detrital particles of river sediments within a glacial catchment at the northeastern Pamir Plateau, in order to understand sediment transfer mechanism and to test feasibility of U-series comminution model in a glacial environment.Materials and methods The study was performed within the Gaizi River catchment in the northeastern Pamir Plateau, owing to its significant elevation gradient and climate difference. The upper reaches of the Gaizi River catchment are extensively covered with glaciers. Sixteen river sediment samples were collected along the major tributaries and mainstream of the Gaizi River. The mineralogy of samples was determined by XRD, ~(234)U/~(238)U activity ratio((~(234)U/~(238)U)_(AR)) of fine detrital particles by MC-ICP-MS and particle BET surface areas by nitrogen adsorption-desorption instrument. Results The mineralogical compositions of river sediments are dominated by quartz and feldspar(accounting for 51% — 77%), indicating a weak weathering. The measured(~(234)U/~(238)U)_(AR) are high, ranging from 0.988 to 1.017 in river sediments from the upstream Kangxiwa and Muji tributaries, whereas the ratios decreased in the middle and lower reaches of the Gaizi River, ranging from 0.913 to 0.997. However,the recoil loss factors fα calculated by particle specific surface areas of the typical samples are much lower than the theoretical minimum values. Discussion The measured(~(234)U/~(238)U)_(AR) of fine detrital particles in the upstream mountains are slightly larger than or close to the values of fresh rocks in secular equilibrium((~(234)U/~(238)U)_(AR) =1.00 ± 0.01), reflecting rapid erosion process within a glacial environment. On the one hand, the(~(234)U/~(238)U)_(AR) of fine detrital particles show a decreased trend from the upstream to the lower reaches within the Gaizi River catchment, indicating the release of ~(234)U during sediment transport. On the other hand, similar to some higherosion catchments, the low particle SBET specific surface areas of detrital particles in a glacial environment lead to an unreasonable transport time by the U-series comminution model. Conclusions Due to rapid erosion within the Gaizi glacial catchment, the measured(~(234)U/~(238)U)_(AR) of fine detrital particles in the upstream mountains can be served as an endmember of initial(~(234)U/~(238)U)_(AR) of fresh rocks. Although transport time cannot be obtained from the comminution age equation owing to low particle surface area, a decrease in(~(234)U/~(238)U)_(AR) ratios from the upstream to the lower reaches within the Gaizi River catchment still proves the robustness of the U-series isotopes in tracing sediment transport processes. Recommendations and perspectives We argued that the assumption of secular equilibrium of(~(234)U/~(238)U)_(AR) = 1.00 ± 0.01 may need further work to estimate for the endmember of initial(~(234)U/~(238)U)_(AR). The fine detrital particles in glacial catchments may not be suitable for the application of the U-series comminution model, but further work is worthy to test its feasibility in various geological and climatic settings.
Background, aim, and scope The uranium(U)-series isotopes are recently used in the study of the transport processes of terrestrial and marine sediments as one of new geochemical approaches. However, how to use this new approach effectively to trace sediment transport processes still needs more supporting data from various geological and climatic settings. In this study, we analyzed mineralogy and U-series isotopes of fine detrital particles of river sediments within a glacial catchment at the northeastern Pamir Plateau, in order to understand sediment transfer mechanism and to test feasibility of U-series comminution model in a glacial environment.Materials and methods The study was performed within the Gaizi River catchment in the northeastern Pamir Plateau, owing to its significant elevation gradient and climate difference. The upper reaches of the Gaizi River catchment are extensively covered with glaciers. Sixteen river sediment samples were collected along the major tributaries and mainstream of the Gaizi River. The mineralogy of samples was determined by XRD, ~(234)U/~(238)U activity ratio((~(234)U/~(238)U)_(AR)) of fine detrital particles by MC-ICP-MS and particle BET surface areas by nitrogen adsorption-desorption instrument. Results The mineralogical compositions of river sediments are dominated by quartz and feldspar(accounting for 51% — 77%), indicating a weak weathering. The measured(~(234)U/~(238)U)_(AR) are high, ranging from 0.988 to 1.017 in river sediments from the upstream Kangxiwa and Muji tributaries, whereas the ratios decreased in the middle and lower reaches of the Gaizi River, ranging from 0.913 to 0.997. However,the recoil loss factors fα calculated by particle specific surface areas of the typical samples are much lower than the theoretical minimum values. Discussion The measured(~(234)U/~(238)U)_(AR) of fine detrital particles in the upstream mountains are slightly larger than or close to the values of fresh rocks in secular equilibrium((~(234)U/~(238)U)_(AR) =1.00 ± 0.01), reflecting rapid erosion process within a glacial environment. On the one hand, the(~(234)U/~(238)U)_(AR) of fine detrital particles show a decreased trend from the upstream to the lower reaches within the Gaizi River catchment, indicating the release of ~(234)U during sediment transport. On the other hand, similar to some higherosion catchments, the low particle SBET specific surface areas of detrital particles in a glacial environment lead to an unreasonable transport time by the U-series comminution model. Conclusions Due to rapid erosion within the Gaizi glacial catchment, the measured(~(234)U/~(238)U)_(AR) of fine detrital particles in the upstream mountains can be served as an endmember of initial(~(234)U/~(238)U)_(AR) of fresh rocks. Although transport time cannot be obtained from the comminution age equation owing to low particle surface area, a decrease in(~(234)U/~(238)U)_(AR) ratios from the upstream to the lower reaches within the Gaizi River catchment still proves the robustness of the U-series isotopes in tracing sediment transport processes. Recommendations and perspectives We argued that the assumption of secular equilibrium of(~(234)U/~(238)U)_(AR) = 1.00 ± 0.01 may need further work to estimate for the endmember of initial(~(234)U/~(238)U)_(AR). The fine detrital particles in glacial catchments may not be suitable for the application of the U-series comminution model, but further work is worthy to test its feasibility in various geological and climatic settings.
引文
李燕,李红斌,王连有.2003.喀喇昆仑山盖孜河水文水资源特性分析[J].干旱区研究,20(4):272-275.[Li Y,Li H B,Wang L Y.2003.Analysis on the hydrology and water resources of Gez River in Karakorum Mountain[J].Arid Zone Research,20(4):272-275.]
毛炜峄,孙本国,王铁,等.2006.近50年来喀什噶尔河流域气温、降水及径流的变化趋势[J].干旱区研究,23(4):531-538.[Mao W Y,Sun B G,Wang T,et al.2006.Change trends of temperature,precipitation and runoff volume in the Kaxgar River basin since recent 50 years[J].Arid Zone Research,23(4):531-538.]
冉钊.2009.布伦口地区河流阶地研究[D].焦作:河南理工大学.[Ran Z.2009.The study of river terraces in the Bulunkou area[D].Jiaozuo:Henan Polytechnic University.]
杨清理,翟伟,阎平,等.2012.中国帕米尔高原喀拉库勒湖地区的植物物种多样性[J].江苏农业科学,40(2):259-261.[Yang Q L,Zhai W,Yan P,et al.2012.The diversity of plant species in the Karakul Lake region of Pamir Plateau,China[J].Jiangsu Agricultural Sciences,40(2):259-261.]
殷铎,金章东,张飞,等.2016.喀拉库里表层沉积物组成的分布特征及其物质来源[J].地球环境学报,7(4):380-392.[Yin D,Jin Z D,Zhang F,et al.2016.Spatial distribution of surface lake sediment compositions in Kala Kul Lake and its implications for provenances[J].Journal of Earth Environment,7(4):380-392.]
曾磊,杨太保,田洪阵.2013.近40年东帕米尔高原冰川变化及其对气候的响应[J].干旱区资源与环境,27(5):144-150.[Zeng L,Yang T B,Tian H Z.2013.Response of glacier variations in the Eastern Pamirs Plateau to climate change,during the last 40 years[J].Journal of Arid Land Resources and Evironment,27(5):144-150.]
张瑞江.2010.卡拉库勒湖成因的遥感分析[J].国土资源遥感,(S1):69-71.[Zhang R J.2010.A genetic analysis of the Karakul Lake based on remote sensing images[J].Remote Sensing for Land&Resources,(S1):69-71.]
中国科学院寒区旱区环境与工程研究所.2001.中国冰川目录Ⅳ:帕米尔山区(喀什噶尔河等流域)[M].修订本.兰州:甘肃文化出版社.[Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences.2001.Glacier inventory of ChinaⅣ:Pamirs(drainage basins of Kaxgar River and others)[M].Revised ed.Lanzhou:Gansu Culture Publishing House.]
Aciego S,Bourdon B,Schwander J,et al.2011.Toward a radiometric ice clock:uranium ages of the Dome Cice core[J].Quaternary Science Reviews,30(19/20):2389-2397.
Avnir D,Jaroniec M.1989.An isotherm equation for adsorption on fractal surfaces of heterogeneous porous materials[J].Langmuir,5(6):1431-1433.
Bourdon B,Bureau S,Andersen M B,et al.2009.Weathering rates from top to bottom in a carbonate environment[J].Chemical Geology,258(3/4):275-287.
Bourdon B,Turner S,Henderson G M,et al.2003.Introduction to U-series geochemistry[J].Reviews in Mineralogy&Geochemistry,52(1):1-21.
Chabaux F,Blaes E,Granet M,et al.2012.Determination of transfer time for sediments in alluvial plains using238U-234U-230Th disequilibria:The case of the Ganges river system[J].Comptes Rendus Geoscience,344(11/12):688-703.
Dadson S J,Hovius N,Chen H,et al.2003.Links between erosion,runoff variability and seismicity in the Taiwan orogen[J].Nature,426(6967):648-651.
DePaolo D J,Lee V E,Christensen J N,et al.2012.Uranium comminution ages:Sediment transport and deposition time scales[J].Comptes Rendus Geoscience,344(11/12):678-687.
DePaolo D J,Maher K,Christensen J N,et al.2006.Sediment transport time measured with U-series isotopes:results from ODP North Atlantic drift site 984[J].Earth and Planetary Science Letters,248(1/2):394-410.
Dosseto A,Bourdon B,Turner S P.2008.Uranium-series isotopes in river materials:Insights into the timescales of erosion and sediment transport[J].Earth and Planetary Science Letters,265(1/2):1-17.
Dosseto A,Bourdon B,Gaillardet J,et al.2006.Weathering and transport of sediments in the Bolivian Andes:time constraints from uranium-series isotopes[J].Earth and Planetary Science Letters,248(3/4):759-771.
Gascoyne M,Miller N H,Neymark L A.2002.Uranium-series disequilibrium in tuffs from Yucca Mountain,Nevada,as evidence of pore-fluid flow over the last million years[J].Applied Geochemistry,17(6):781-792.
Granet M,Chabaux F,Stille P,et al.2007.Time-scales of sedimentary transfer and weathering processes from U-series nuclides:Clues from the Himalayan rivers[J].Earth and Planetary Science Letters,261(3/4):389-406.
Handley H K,Turner S,Afonso J C,et al.2013.Sediment residence times constrained by uranium-series isotopes:a critical appraisal of the comminution approach[J].Geochimica et Cosmochimica Acta,103:245-262.
Herman F,Seward D,Valla P G,et al.2013.Worldwide acceleration of mountain erosion under a cooling climate[J].Nature,504(7480):423-426.
Larsen I J,Montgomery D R,Greenberg H M.2014.The contribution of mountains to global denudation[J].Geology,42(6):527-530.
Lee V E,DePaolo D J,Christensen J N.2010.Uranium-series comminution ages of continental sediments:case study of a Pleistocene alluvial fan[J].Earth and Planetary Science Letters,296(3/4):244-254.
Li C,Yang S Y,Lian E G,et al.2015.A review of comminution age method and its potential application in the East China Sea to constrain the time scale of sediment source-to-sink process[J].Journal of Ocean University of China,14(3):399-406.
Li G,West A J,Densmore A L,et al.2017b.Earthquakes drive focused denudation along a tectonically active mountain front[J].Earth and Planetary Science Letters,472:253-265.
Li L,Liu X J,Li T,et al.2017a.Uranium comminution age tested by the eolian deposits on the Chinese Loess Plateau[J].Earth and Planetary Science Letters,467:64-71.
Maher K,DePaolo D J,Christensen J N.2006.U-Sr isotopic speedometer:Fluid flow and chemical weathering rates in aquifers[J].Geochimica et Cosmochimica Acta,70(17):4417-4435.
Martin A N,Dosseto A,Kinsley L P J.2015.Evaluating the removal of non-detrital matter from soils and sediment using uranium isotopes[J].Chemical Geology,396:124-133.
Rudnick R L,Gao S.2003.The composition of the continental crust[M]//Rudnick R L.The crust,vol.3,treatise on geochemistry.Oxford:Elsevier:1-64.
Suresh P O,Dosseto A,Handley H K,et al.2014.Assessment of a sequential phase extraction procedure for uraniumseries isotope analysis of soils and sediments[J].Applied Radiation and Isotopes,83:47-55.
Tapponnier P,Peltzer G,Le Dain A Y,et al.1982.Propagating extrusion tectonics in Asia:New insights from simple experiments with plasticine[J].Geology,10(12):611-616.
Vigier N,Burton K W,Gislason S R,et al.2006.The relationship between riverine U-series disequilibria and erosion rates in a basaltic terrain[J].Earth and Planetary Science Letters,249(3/4):258-273.
Xu B Q,Yao T D,Lu A X,et al.2006.Variations of nearsurface atmospheric CO2 and H2O concentrations during summer on Mustagata[J].Science in China(Series D:Earth Sciences),49(1):18-26.
Zhang W F,Chen J,Ji J F,et al.2016.Evolving flux of Asian dust in the north Pacific Ocean since the late Oligocene[J].Aeolian Research,23:11-20.
毛炜峄,孙本国,王铁,等.2006.近50年来喀什噶尔河流域气温、降水及径流的变化趋势[J].干旱区研究,23(4):531-538.[Mao W Y,Sun B G,Wang T,et al.2006.Change trends of temperature,precipitation and runoff volume in the Kaxgar River basin since recent 50 years[J].Arid Zone Research,23(4):531-538.]
冉钊.2009.布伦口地区河流阶地研究[D].焦作:河南理工大学.[Ran Z.2009.The study of river terraces in the Bulunkou area[D].Jiaozuo:Henan Polytechnic University.]
杨清理,翟伟,阎平,等.2012.中国帕米尔高原喀拉库勒湖地区的植物物种多样性[J].江苏农业科学,40(2):259-261.[Yang Q L,Zhai W,Yan P,et al.2012.The diversity of plant species in the Karakul Lake region of Pamir Plateau,China[J].Jiangsu Agricultural Sciences,40(2):259-261.]
殷铎,金章东,张飞,等.2016.喀拉库里表层沉积物组成的分布特征及其物质来源[J].地球环境学报,7(4):380-392.[Yin D,Jin Z D,Zhang F,et al.2016.Spatial distribution of surface lake sediment compositions in Kala Kul Lake and its implications for provenances[J].Journal of Earth Environment,7(4):380-392.]
曾磊,杨太保,田洪阵.2013.近40年东帕米尔高原冰川变化及其对气候的响应[J].干旱区资源与环境,27(5):144-150.[Zeng L,Yang T B,Tian H Z.2013.Response of glacier variations in the Eastern Pamirs Plateau to climate change,during the last 40 years[J].Journal of Arid Land Resources and Evironment,27(5):144-150.]
张瑞江.2010.卡拉库勒湖成因的遥感分析[J].国土资源遥感,(S1):69-71.[Zhang R J.2010.A genetic analysis of the Karakul Lake based on remote sensing images[J].Remote Sensing for Land&Resources,(S1):69-71.]
中国科学院寒区旱区环境与工程研究所.2001.中国冰川目录Ⅳ:帕米尔山区(喀什噶尔河等流域)[M].修订本.兰州:甘肃文化出版社.[Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences.2001.Glacier inventory of ChinaⅣ:Pamirs(drainage basins of Kaxgar River and others)[M].Revised ed.Lanzhou:Gansu Culture Publishing House.]
Aciego S,Bourdon B,Schwander J,et al.2011.Toward a radiometric ice clock:uranium ages of the Dome Cice core[J].Quaternary Science Reviews,30(19/20):2389-2397.
Avnir D,Jaroniec M.1989.An isotherm equation for adsorption on fractal surfaces of heterogeneous porous materials[J].Langmuir,5(6):1431-1433.
Bourdon B,Bureau S,Andersen M B,et al.2009.Weathering rates from top to bottom in a carbonate environment[J].Chemical Geology,258(3/4):275-287.
Bourdon B,Turner S,Henderson G M,et al.2003.Introduction to U-series geochemistry[J].Reviews in Mineralogy&Geochemistry,52(1):1-21.
Chabaux F,Blaes E,Granet M,et al.2012.Determination of transfer time for sediments in alluvial plains using238U-234U-230Th disequilibria:The case of the Ganges river system[J].Comptes Rendus Geoscience,344(11/12):688-703.
Dadson S J,Hovius N,Chen H,et al.2003.Links between erosion,runoff variability and seismicity in the Taiwan orogen[J].Nature,426(6967):648-651.
DePaolo D J,Lee V E,Christensen J N,et al.2012.Uranium comminution ages:Sediment transport and deposition time scales[J].Comptes Rendus Geoscience,344(11/12):678-687.
DePaolo D J,Maher K,Christensen J N,et al.2006.Sediment transport time measured with U-series isotopes:results from ODP North Atlantic drift site 984[J].Earth and Planetary Science Letters,248(1/2):394-410.
Dosseto A,Bourdon B,Turner S P.2008.Uranium-series isotopes in river materials:Insights into the timescales of erosion and sediment transport[J].Earth and Planetary Science Letters,265(1/2):1-17.
Dosseto A,Bourdon B,Gaillardet J,et al.2006.Weathering and transport of sediments in the Bolivian Andes:time constraints from uranium-series isotopes[J].Earth and Planetary Science Letters,248(3/4):759-771.
Gascoyne M,Miller N H,Neymark L A.2002.Uranium-series disequilibrium in tuffs from Yucca Mountain,Nevada,as evidence of pore-fluid flow over the last million years[J].Applied Geochemistry,17(6):781-792.
Granet M,Chabaux F,Stille P,et al.2007.Time-scales of sedimentary transfer and weathering processes from U-series nuclides:Clues from the Himalayan rivers[J].Earth and Planetary Science Letters,261(3/4):389-406.
Handley H K,Turner S,Afonso J C,et al.2013.Sediment residence times constrained by uranium-series isotopes:a critical appraisal of the comminution approach[J].Geochimica et Cosmochimica Acta,103:245-262.
Herman F,Seward D,Valla P G,et al.2013.Worldwide acceleration of mountain erosion under a cooling climate[J].Nature,504(7480):423-426.
Larsen I J,Montgomery D R,Greenberg H M.2014.The contribution of mountains to global denudation[J].Geology,42(6):527-530.
Lee V E,DePaolo D J,Christensen J N.2010.Uranium-series comminution ages of continental sediments:case study of a Pleistocene alluvial fan[J].Earth and Planetary Science Letters,296(3/4):244-254.
Li C,Yang S Y,Lian E G,et al.2015.A review of comminution age method and its potential application in the East China Sea to constrain the time scale of sediment source-to-sink process[J].Journal of Ocean University of China,14(3):399-406.
Li G,West A J,Densmore A L,et al.2017b.Earthquakes drive focused denudation along a tectonically active mountain front[J].Earth and Planetary Science Letters,472:253-265.
Li L,Liu X J,Li T,et al.2017a.Uranium comminution age tested by the eolian deposits on the Chinese Loess Plateau[J].Earth and Planetary Science Letters,467:64-71.
Maher K,DePaolo D J,Christensen J N.2006.U-Sr isotopic speedometer:Fluid flow and chemical weathering rates in aquifers[J].Geochimica et Cosmochimica Acta,70(17):4417-4435.
Martin A N,Dosseto A,Kinsley L P J.2015.Evaluating the removal of non-detrital matter from soils and sediment using uranium isotopes[J].Chemical Geology,396:124-133.
Rudnick R L,Gao S.2003.The composition of the continental crust[M]//Rudnick R L.The crust,vol.3,treatise on geochemistry.Oxford:Elsevier:1-64.
Suresh P O,Dosseto A,Handley H K,et al.2014.Assessment of a sequential phase extraction procedure for uraniumseries isotope analysis of soils and sediments[J].Applied Radiation and Isotopes,83:47-55.
Tapponnier P,Peltzer G,Le Dain A Y,et al.1982.Propagating extrusion tectonics in Asia:New insights from simple experiments with plasticine[J].Geology,10(12):611-616.
Vigier N,Burton K W,Gislason S R,et al.2006.The relationship between riverine U-series disequilibria and erosion rates in a basaltic terrain[J].Earth and Planetary Science Letters,249(3/4):258-273.
Xu B Q,Yao T D,Lu A X,et al.2006.Variations of nearsurface atmospheric CO2 and H2O concentrations during summer on Mustagata[J].Science in China(Series D:Earth Sciences),49(1):18-26.
Zhang W F,Chen J,Ji J F,et al.2016.Evolving flux of Asian dust in the north Pacific Ocean since the late Oligocene[J].Aeolian Research,23:11-20.
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