Chemical erosion in the eastern Himalaya: Major ion composition of the Brahmaputra and δ13C of dissolved inorganic carbon
Chemical erosion in the eastern Himalaya: Major ion composition of the Brahmaputra and δ13C of dissolved inorganic carbon
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DOI：
10.1016/j.gca.2005.02.033
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发表时间：
2005-07
影响因子：
5
通讯作者：
Sunil Kumar Singh;M. Sarin;C. France‐Lanord
中科院分区：
文献类型：
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作者：
Sunil Kumar Singh;M. Sarin;C. France‐Lanord
测量了喜马拉雅东部布拉马普特拉河水系（印度和孟加拉国流域）水的主要离子组成、DIC（溶解无机碳）的δ13C和河岸沉积物的粘土矿物组成，以了解化学风化和侵蚀以及控制这些过程的因素。从雅鲁藏布江干流中每两周采集一次的古瓦哈蒂时间序列样本也被分析了主要离子组成。沉积物的粘土矿物学和蚀变化学指数（CIA）表明，与恒河盆地相比，该地区风化强度相对较弱。这是由于雅鲁藏布江流域的径流量增加和相关的物理侵蚀造成的。研究结果首次揭示了雅鲁藏布江流域化学侵蚀速率和硅酸盐侵蚀速率的时空变化规律。雅鲁藏布江流域的子盆地表现出大约一个数量级的化学侵蚀速率变化。东结滑盆地以约300 t km - 2y - 1的侵蚀速率占主导地位，是世界河流流域中最高的之一，与一些玄武岩地形的侵蚀速率相当。相比之下，平坦、寒冷和相对干旱的西藏盆地经历的化学侵蚀要慢得多（约40 t km−2y−1）。在一年时间序列样品中，总溶解固体丰度（TDS, 102 ~ 203mg /L）随年流量的变化而变化，但其中有一个可归因于山洪暴发。Na* （Na经旋回成分校正）与Si呈强正相关，表明它们的共同来源为硅酸盐风化。对硅酸盐阳离子（Nasil+Ksil+Casil+Mgsil）的估计表明，雅鲁藏布江中约有一半的溶解阳离子来自硅酸盐，这一比例高于恒河系统。雅鲁藏布江流域硅酸盐风化作用的co2消耗速率为~ 6 × 105mol km−2y−1；而在东部合槽次盆地中，这一数值为~ 19 × 105mol km−2y−1，与某些玄武岩地形的估算值相似。研究表明，雅鲁藏布江东部合槽盆地是全球化学侵蚀最强烈的地区之一；径流和物理侵蚀是东喜马拉雅地区化学侵蚀的控制因素。
Major ion composition of waters, δ13C of its DIC (dissolved inorganic carbon), and the clay mineral composition of bank sediments in the Brahmaputra River System (draining India and Bangladesh) have been measured to understand chemical weathering and erosion and the factors controlling these processes in the eastern Himalaya. The time-series samples, collected biweekly at Guwahati, from the Brahmaputra mainstream, were also analyzed for the major ion composition. Clay mineralogy and chemical index of alteration (CIA) of sediments suggest that weathering intensity is relatively poor in comparison to that in the Ganga basin. This is attributed to higher runoff and associated physical erosion occurring in the Brahmaputra basin. The results of this study show, for the first time, spatial and temporal variations in chemical and silicate erosion rates in the Brahmaputra basin. The subbasins of the Brahmaputra watershed exhibit chemical erosion rates varying by about an order of magnitude. The Eastern Syntaxis basin dominates the erosion with a rate of ∼300 t km−2y−1, one of the highest among the world river basins and comparable to those reported for some of the basaltic terrains. In contrast, the flat, cold, and relatively more arid Tibetan basin undergoes much slower chemical erosion (∼40 t km−2y−1). The abundance of total dissolved solids (TDS, 102–203 mg/L) in the time-series samples collected over a period of one year shows variations in accordance with the annual discharge, except one of them, cause for which is attributable to flash floods. Na* (Na corrected for cyclic component) shows a strong positive correlation with Si, indicating their common source: silicate weathering. Estimates of silicate cations (Nasil+Ksil+Casil+Mgsil) suggest that about half of the dissolved cations in the Brahmaputra are derived from silicates, a proportion higher than that for the Ganga system. The CO2consumption rate due to silicate weathering in the Brahmaputra watershed is ∼6 × 105moles km−2y−1; whereas that in the Eastern Syntaxis subbasin is ∼19 × 105moles km−2y−1, similar to the estimates for some of the basaltic terrains. This study suggests that the Eastern Syntaxis basin of the Brahmaputra is one of most intensely chemically eroding regions of the globe; and that runoff and physical erosion are the controlling factors of chemical erosion in the eastern Himalaya.