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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Weathering Control over Geomorphology of Supermature Proterozoic Delhi Quartzites of India
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Weathering Control over Geomorphology of Supermature Proterozoic Delhi Quartzites of India

机译：印度高级元古代德里石英岩地貌的风化控制

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摘要

Quartz and quartzite are thought to be resistant as a mineral and a rock respectively; however, we have shown that the presence of small amounts of pyrite in the quartzites makes them vulnerable to weathering. We observe that weathering of Proterozoic quartzite in the semi-arid conditions around Delhi proceeded from fractures towards the inside and produced weathering rinds. The chemical index of alteration (CIA), which is actually a measure of weathering of aluminosilicate minerals, increases from the core outwards, through the rinds. Although aluminosilicate minerals occur only as minor phases (<2 per cent), their weathering indicates a movement of the weathering front from the periphery towards the core. We have suggested a coupled mechanism in which the dissolution of pyrites by moving water produced a sulphate-bearing acidic solution and ferrous iron, which reacted with aluminosilicate minerals and quartz, respectively. This initially makes the Delhi quartzite porous and subsequently friable. The total disintegration of grain to grain contacts imparted friability to this quartzite to produced silica sand. Subsequent physical erosion of loose sand, produced during rind development in the outermost zones, has given rise to features like tors, spheroids, gullies, cavities and small-scale caves on these quartzites. Thus, the terrain has acquired ruggedness in semi-arid conditions.
机译：石英和石英岩分别被认为是抗矿物和岩石的。然而，我们已经表明，石英岩中少量黄铁矿的存在使其容易遭受风化。我们观察到，在德里附近的半干旱条件下，元古代石英岩的风化从裂缝向内部发展，并产生风化外皮。化学变化指数（CIA）实际上是铝硅酸盐矿物风化的量度，从核心向外通过果皮逐渐增加。尽管硅铝酸盐矿物仅以次要阶段出现（<2％），但它们的风化表明风化锋面从外围向岩心移动。我们提出了一种耦合机制，其中通过移动水来分解黄铁矿会生成含硫酸盐的酸性溶液和亚铁，它们分别与铝硅酸盐矿物和石英反应。最初使德里石英岩多孔，然后变得易碎。晶粒到晶粒接触的总崩解赋予该石英岩脆性以产生硅砂。随后在最外围区域的果皮发育过程中产生的疏松沙子物理侵蚀，使这些石英岩上出现了诸如扭力，椭球，沟壑，空腔和小规模洞穴等特征。因此，地形在半干旱条件下具有坚固性。

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