福建长乐屏山风化坑与河流壶穴的成因及其证据
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摘要
风化坑和壶穴是一种常见的岩石坑穴地形,其形成原因和形态完全不同,但容易被误解和混淆。结合对福建长乐三溪河地区这两种坑穴地形的实地考察,本文从地貌学,沉积学,岩石化学和矿物学等各个方面对两者的形成过程、影响因素进行了论证和对比。研究表明:风化坑形成于岩石面积水的风化作用,壶穴则是由河流的旋转水流对河床产生的侵蚀作用形成;山顶风化坑的发育与河流流水作用没有关系,河流壶穴的形成与河谷的发育过程有关,河谷中的风化坑只能在河流深切后,流水不再作用到的河床部位发育;只要条件合适,风化坑或壶穴随时可以生成;风化坑与河流壶穴的形态,坑内沉积物的磨圆度、粒度特征等反映出各自不同的形成过程。风化坑内碎屑与周边岩石的化学蚀变指数CIA值的差异反映了风化坑的化学风化成因;风化坑内碎屑与周边岩石石英长石比例的差异说明风化坑是矿物差异风化的结果;用CIA值和英长比均无法区分河流壶穴和风化坑中的碎屑颗粒,但两者化学元素迁移特征的差别反映了风化坑的风化作用和河流壶穴的流水搬运作用的成因差别;风化坑的风化程度达不到当地风化壳的风化程度,但不同气候带风化坑碎屑的CIA值能反映不同气候带风化作用的强度差异。
In Sanxi river area of Changle of Fujian province, there are some pits developed in granitic rock on the top of mountains and the surface of river beds. Such pits known as mountain top glacial potholes or river valley glacial potholes have been considered to be typical glacial potholes, which were used to support the evidence that the Quaternary glacier has been extended to the area of Fujian Province, China. The field investigation for these pits we made in March 2011 shows that the pits are weathering pits or river potholes, instead of glacial potholes. In this paper, the origin and formation process, as well as the related influencing factors, of the weathering pits and the river potholes developed in this area were studied and compared from the aspects of geomorphology, sedimentology, petrochemistry and mineralogy. The studies show that the formation of the river potholes is due to the mechanical erosion of stream water while that of the weathering pits on the top of mountains has nothing to do with river water but is the water standing in rock surface depression that results in chemical weathering. The weathering pits may also be found in river valleys, but can be only developed in the positions where the river water could not be reached after a river incision. The potholes and the weathering pits are morphologically distinct with particles of different roundness and grain sizes, denoting the different formation processes generated by chemical weathering or mechanical erosion. The different CIA values and the different quartz to feldspar ratios between the particles in the weathering pits and the rock where the pits were formed could be used to indicate the results of chemical weathering and mineral differential weathering. The river potholes also have different CIA values or quartz to feldspar ratios between the particles and the rocks as the weathering pits, and then the value and the ratio could not be used to distinguish the potholes from the weathering pits. However, the river potholes have a chemical element migration between the rocks and the particles, which is very different from that of the weathering pits, reflecting the processes of the particle transportation by river water in the potholes and the chemical weathering in the weathering pits.
In Sanxi river area of Changle of Fujian province, there are some pits developed in granitic rock on the top of mountains and the surface of river beds. Such pits known as mountain top glacial potholes or river valley glacial potholes have been considered to be typical glacial potholes, which were used to support the evidence that the Quaternary glacier has been extended to the area of Fujian Province, China. The field investigation for these pits we made in March 2011 shows that the pits are weathering pits or river potholes, instead of glacial potholes. In this paper, the origin and formation process, as well as the related influencing factors, of the weathering pits and the river potholes developed in this area were studied and compared from the aspects of geomorphology, sedimentology, petrochemistry and mineralogy. The studies show that the formation of the river potholes is due to the mechanical erosion of stream water while that of the weathering pits on the top of mountains has nothing to do with river water but is the water standing in rock surface depression that results in chemical weathering. The weathering pits may also be found in river valleys, but can be only developed in the positions where the river water could not be reached after a river incision. The potholes and the weathering pits are morphologically distinct with particles of different roundness and grain sizes, denoting the different formation processes generated by chemical weathering or mechanical erosion. The different CIA values and the different quartz to feldspar ratios between the particles in the weathering pits and the rock where the pits were formed could be used to indicate the results of chemical weathering and mineral differential weathering. The river potholes also have different CIA values or quartz to feldspar ratios between the particles and the rocks as the weathering pits, and then the value and the ratio could not be used to distinguish the potholes from the weathering pits. However, the river potholes have a chemical element migration between the rocks and the particles, which is very different from that of the weathering pits, reflecting the processes of the particle transportation by river water in the potholes and the chemical weathering in the weathering pits.
引文
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[14]Li Xianhua,Qi Changshi,Liu Ying et al.Petrogenesis of the Neopro-terozoic bimodal volcanic rocks along the western margin of the Yangtze Block:New constraints from Hf isotopes and Fe/Mn ratios.Chinese Science Bulletin,2005,50(21):2481-2486.
[15]Nesbitt H W,Young G M.Early Proterozoic climates and plate motions inferred from major element chemistry of lutites.Nature,1982,299:715-717.
[16]McLennan S M.Weathering and global denudation.The Journal of Geology,1993,101(2):295-303.
[17]Nesbitt H W.Mobility and fractionation of rare earth elements during weathering of a granodiorite.Nature,1979,279:206-210.
[18]Chen Jun,Ji Junfeng,Qiu Gang et a1.Geochemistry of the chemical weathering intensity of the loess profile in Luochuan,Shaanxi Province.Science in China:Series D,1997,27(6):531-536.[陈骏,季峻峰,仇纲等.陕西洛川黄土化学风化程度的地球化学研究.中国科学:D辑,1997,27(6):531-536.]
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[21]Huang Zhenguo,Zhang Weiqiang,Chen Junhong et al.Red Weathering Crust in Southern China.Beijing:China Ocean Press,1996:38-57;127-134.[黄镇国,张伟强,陈俊鸿等.中国南方红色风化壳.北京:海洋出版社,1996:38-57;127-134.]
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[24]Twidale C R.Weather pit(Gnamma).Australian Geographer,1965,9(5):318-319.
[25]Villar D D.Early formation of gnammas(weathering pits)in a recently glaciated area of Torresdel Paine,southern Patagonia(Chile).Geomorphology,2006,76(1/2):137-147.
[26]Springer G S,Tools T,Wohl T T.Theoretical modeling of stream potholes based upon empirical observations from the Orange River,Republic of South Africa.Geomorphology,2006,82(1/2):160-176.
[27]Lorenc M W,Barco P M,Saavedra J.The evolution of potholes in granite bedrock,W Spain.Catena,1994,22:265-274.
[28]Wang Wei,Huang Shan,Liang Mingzhu.Formation and development of the potholes formed in a gorge river in Guangdong.Acta Geographica Sinica,2007,62(7):691-697.[王为,黄山,梁明珠.广东大峡谷河床壶穴形态的形成与发育.地理学报,2007,62(7):691-697.]
[29]Lewis D W.Practical Sedimentology.Pennsylvania:Hutchinson Ross Publishing Company,1983:64-66.
[30]Wang Wei,Zhou Shangzhe,Li Bingyuan et al.Petrochemistry and mineralogy evidences for the weathering process of the weathering pits on rock surfaces of Mountain Loashan,China.Quaternary Sciences,2012,32(1):158-166.[王为,周尚哲,李炳元等.崂山山顶风化坑化学风化过程的岩石化学与矿物学证据.第四纪研究,2012,32(1):158-166.]
[31]McLennan S M.Weathering and global denudation.The Journal of Geology,1993,101(2):295-303.
[32]ПолыновББ.Weathering Crust and Its Earth Chemistry.Chen Jingsheng trans.Beijing:The Commercial Press,1959:28-39;80-84.[波雷诺夫.风化壳及其地球化学.陈静生译.北京:商务印书馆,1959:28-39;80-84.]
[1]Goudie A S.Weathering pits//Goudie A S.Encyclopedia of Geomorphology.New York:Routledge,2004.
[2]Twidale C R,Romani J R V.Landforms and Geology of Granite Terrains.London:Taylor&Francis,2005:207-234.
[3]Migon P.Granite Landscapes of the World.New York:Oxford University Press,2006:132-160.
[4]Alexander H S.Pothole erosion.Journal of Geology,1932,40(4):305-337.
[5]Whipple K X,Hancock G S,Anderson R S.River incision into bedrock:Mechanics and relative efficacy of plucking,abrasion,and cavitation.Geological Society of America Bulletin,2000,112(3):490-503.
[6]Richardson K,Carling P A.A typology of sculpted forms in open bedrock channels.Geological Society of America Special Papers,2005,392:1-108.
[7]Han Tongli.Moulin Discovered.Beijing:Huaxia Publishing House,2004:1-190.[韩同林.发现冰臼.北京:华夏出版社,2004:1-190.]
[8]Wu Kelong,Yan Pingquan,Lu Zhengqiu et al.The general features of the miarolitie(potash)granites in Fujian Province and the preliminary discussion on their origin.Geology of Fujian,1982,(1):1-28[吴克隆,严炳拴,陆振球等.福建省晶洞(钾长)花岗岩一般特征及成因初步讨探.福建地质,1982,(1):1-28.]
[9]Ma Lifang.Geological Atlas of China.Beijing:Geological Publishing House,2002:253-260.[马丽芳.中国地质图集.北京:地质出版社,2002:253-256.]
[10]Geography Department of Fujian Normal University.Physical Geography of Fujian.Fuzhou:Fujian People's Publishing Press,1987:1-209.[福建师范大学地理系《福建自然地理》编写组.福建自然地理.福州:福建人民出版社,1987:1-209.]
[11]Andrade F,Ferreira M A.A simple method of measuring beach profiles.Journal of Coastal Research,2006,22(4):995-999.
[12]Cheng Guaiming,Qi Hongyu,Pan Wei.Matlab(6.X)for Mathematical Statistics.Beijing:Science Press,2002.[陈桂明,戚红雨,潘伟.MATLAB数理统计(6.X).北京:科学出版社,2002.]
[13]Folk P L,Ward W D.Brazos Reviver bar:A study in the significance of grain size parameters.J.Sed.Petrol.,1957,27(1):3-26
[14]Li Xianhua,Qi Changshi,Liu Ying et al.Petrogenesis of the Neopro-terozoic bimodal volcanic rocks along the western margin of the Yangtze Block:New constraints from Hf isotopes and Fe/Mn ratios.Chinese Science Bulletin,2005,50(21):2481-2486.
[15]Nesbitt H W,Young G M.Early Proterozoic climates and plate motions inferred from major element chemistry of lutites.Nature,1982,299:715-717.
[16]McLennan S M.Weathering and global denudation.The Journal of Geology,1993,101(2):295-303.
[17]Nesbitt H W.Mobility and fractionation of rare earth elements during weathering of a granodiorite.Nature,1979,279:206-210.
[18]Chen Jun,Ji Junfeng,Qiu Gang et a1.Geochemistry of the chemical weathering intensity of the loess profile in Luochuan,Shaanxi Province.Science in China:Series D,1997,27(6):531-536.[陈骏,季峻峰,仇纲等.陕西洛川黄土化学风化程度的地球化学研究.中国科学:D辑,1997,27(6):531-536.]
[19]Kurtz A C,Derry L A,Chadwick O A et al.Refractory element mobility in volcanic soils.Geology,2000,28(8):683-686.
[20]Anderson S P,Dietrich W E,Brimhall G H Jr.Weathering pro fi les,mass balance analysis,and rates of solute loss:Linkages between weathering and erosion in a small,steep catchment:Geological Society of America Bulletin,2002,114(9):1143-1158.
[21]Huang Zhenguo,Zhang Weiqiang,Chen Junhong et al.Red Weathering Crust in Southern China.Beijing:China Ocean Press,1996:38-57;127-134.[黄镇国,张伟强,陈俊鸿等.中国南方红色风化壳.北京:海洋出版社,1996:38-57;127-134.]
[22]Matthes F E.Geological history of the Yosemite Valley.U.S.Geological Survey,Prof.Paper,1930:160.
[23]Smith L L.Weather pits in granite of the southern Piedmont.Journal of Geomorphology,1941,4:117-127.
[24]Twidale C R.Weather pit(Gnamma).Australian Geographer,1965,9(5):318-319.
[25]Villar D D.Early formation of gnammas(weathering pits)in a recently glaciated area of Torresdel Paine,southern Patagonia(Chile).Geomorphology,2006,76(1/2):137-147.
[26]Springer G S,Tools T,Wohl T T.Theoretical modeling of stream potholes based upon empirical observations from the Orange River,Republic of South Africa.Geomorphology,2006,82(1/2):160-176.
[27]Lorenc M W,Barco P M,Saavedra J.The evolution of potholes in granite bedrock,W Spain.Catena,1994,22:265-274.
[28]Wang Wei,Huang Shan,Liang Mingzhu.Formation and development of the potholes formed in a gorge river in Guangdong.Acta Geographica Sinica,2007,62(7):691-697.[王为,黄山,梁明珠.广东大峡谷河床壶穴形态的形成与发育.地理学报,2007,62(7):691-697.]
[29]Lewis D W.Practical Sedimentology.Pennsylvania:Hutchinson Ross Publishing Company,1983:64-66.
[30]Wang Wei,Zhou Shangzhe,Li Bingyuan et al.Petrochemistry and mineralogy evidences for the weathering process of the weathering pits on rock surfaces of Mountain Loashan,China.Quaternary Sciences,2012,32(1):158-166.[王为,周尚哲,李炳元等.崂山山顶风化坑化学风化过程的岩石化学与矿物学证据.第四纪研究,2012,32(1):158-166.]
[31]McLennan S M.Weathering and global denudation.The Journal of Geology,1993,101(2):295-303.
[32]ПолыновББ.Weathering Crust and Its Earth Chemistry.Chen Jingsheng trans.Beijing:The Commercial Press,1959:28-39;80-84.[波雷诺夫.风化壳及其地球化学.陈静生译.北京:商务印书馆,1959:28-39;80-84.]