Pedogenic weathering of tonalite in southern California
Pedogenic weathering of tonalite in southern California
复制标题
南加州英闪长岩的成土风化作用
DOI：
10.1016/0016-7061(70)90055-8
复制
发表时间：
1970
期刊：
影响因子：
6.1
通讯作者：
R. E. Nelson
中科院分区：
文献类型：
--
作者：
W. D. Nettleton;K. Flach;R. E. Nelson
南加州的闪长岩（石英闪长岩）在地中海气候下风化，深度超过30米。在风化过程中，岩石被黑云母风化成蛭石时膨胀而破碎。由此产生的碎片的颗粒密度与岩石相同（2.75 g/cm3）。黑云母占岩石的14%，如果所有的黑云母风化成蛭石，在这种均匀、中等粒度的材料中可以产生1.8%的线性延伸性。实测破碎岩石膨胀率（1 ~ 2%）与预测值吻合。岩石中的其他矿物，大多未风化，有：安山岩，56%；角闪石,13%;石英,9%;正长石，8%研究了某地形层序中4种紧密关联土壤在3种环境下破碎岩对土壤的风化作用。风化环境的差异是土壤地形位置的差异和由此产生的土壤水分状况差异的结果。轻微浸出的环境发生在山顶和后坡位置。这些位置由ustochrets和Haploxeralfs占据。这些土壤的B层碱饱和度低于90%，土壤溶液中缺乏盐，并且含有很少的可交换镁和钠。在这种环境下，蛭石和高岭石由风化的黑云母形成。其他原生矿物中未检出结晶粘土矿物。高钠环境发生在脚坡位置。占据这些位置的钠盐在上部被轻微浸出，但积聚了一些可溶性离子，尤其是钠、镁，在下部的一些地方还积聚了碳酸盐和无定形二氧化硅。在这种环境下，黑云母风化为蛭石和高岭石，安山石和角闪石风化为蒙脱石。第三种环境是一种富含碱基的环境，位于地势较缓且排水受限的地区。在这个位置的培乐沙有大量的可溶性盐和大量的可提取的镁和钠。少量的次生碳酸盐和无定形二氧化硅积聚在它们的太阳下面。在富碱性环境下，黑云母风化为蛭石和蒙脱石，安山石和角闪石风化为贝德尔-蒙脱石。由安山岩形成的贝脱石-蒙脱石为双八面体。其分子式为（Si7.44Al0.56）（Al2.62Mg0.73Fe0.61Ti0.08） O20(OH)4(M+0.95,K+0.05)，电导率为119 mequiv。/ 100 g。原生矿物稳定性由低到高依次为黑云母、安山石、角闪石、石英。
Tonalite (quartz diorite) in southern California has weathered under aa mediterranean climate to depths of more than 30 m. In weathering, the rock was broken up by expansion of biotite as it weathered to vermiculite. The particle density of the resulting fragments is the same as that of the rock (2.75 g/cm3). Biotite comprises 14% of the rock and could produce a linear extensibility of 1.8% in such a uniform, medium-grained material if all the biotite weathered to vermiculite. Measured expansion (1–2%) of the fragmented rock agrees with the predicted value. Other minerals, mostly unweathered, in the rock are: andesine, 56%; hornblende, 13%; quartz, 9%; and orthoclase, 8%.Weathering of the fragmented rock to soil was studied in three kinds of environments in four closely associated soils of a toposequence. Differences in the weathering environments are a result of differences in topographic positions of the soils and resultant differences in soil moisture regimes. A slightly leached environment occurs on hilltop and backslope positions. These position are occupied by Ustochrepts and Haploxeralfs. B horizons of these soils have base saturations of less than 90%, lack salts in soil solution, and contain little exchangeable magnesium and sodium. In this environment vermiculite and kaolinite are formed from weathered biotite. No crystalline clay minerals were detected in the other primary minerals.A high sodium environment occurs in footslope positions. Natrixeralfs occupying these positions are slightly leached in upper parts but accumulate some soluble ions, especially sodium, magnesium, and in places carbonates and amorphous silica in lower parts. In this environment biotite weathers to vermiculite and kaolinite, andesine and hornblende to montmorillonite.The third environment is a base-rich environment found in areas of subdued relief and somewhat restricted drainage. The Pelloxererts in this position have significant amounts of soluble salts and large amounts of extractable magnesium and sodium. Minor amounts of secondary carbonates and amorphous silica accumulate below their sola. In the base-rich environment biotite weathers to vermiculite and montmorillonite, andesine and hornblende to a beidellite-montmorillonite. The beidellite-montmorillonite formed from the andesine is dioctahedral. Its structural formula is (Si7.44Al0.56)(Al2.62Mg0.73Fe0.61Ti0.08) O20(OH)4(M+0.95,K+0.05) and it has a C.E.C. of 119 mequiv./100 g. The stability sequence for primary minerals from least to most stable is biotite, andesine, hornblende, quartz.