The origin of quartz silt, the most abundant detrital particle, is controversial. Quartz silt is generally considered to be broken quartz sand, attributed to glacial, eolian, and/or long fluvial transport. In this article, we highlight the origin of in situ quartz silt in deep weathering profiles (≤7 m) over Precambrian quartzite (>92% quartz with or without 6%–8% mica, feldspar-free), a rock known to be resistant to weathering, in the Shillong Plateau (NE India). This region is one of the most tectonically active and the rainiest place on Earth. We discuss, for the first time, detailed field petrographic and microstructural evidence including diverse microfracturing and dissolution morphologies in quartz, from bedrock through saprolite (2–3 m) and nodular zone (NZ; ∼0.5 m) to soil (≤2–5 m), for quartz silt production through coupled mechanical-chemical processes over 3–4 My in the plateau. Progressive size reduction of quartz from medium sand (1.13–1.36 Φ) in bedrock quartzite through fine sand in saprolite (2.55–2.67 Φ) and the NZ (2.12–4.4 Φ) to coarse and medium silt in soil (4–5 Φ), with concomitant increase in clay mineral (≤80%), characterizes the profiles. Quartzite microfracturing, linked to exhumation and/or seismicity, provided pathways for acidic water to attack and promote chemical weathering in quartz, which in turn effected microfracture widening, porosity enhancement, and weakening of quartz in a positive feedback loop. Mica-microbe interactions facilitated fluid acidity, causing Al and Fe mobilization and more clay mineral production, and enhanced corrosive potential for in situ quartz dissolution in feldspar-free quartzite. Coupled brittle disintegration and chemical weathering of even extremely resistant quartz-rich rocks thus contribute toward long-term regolith development and global quartz silt production.

中文翻译：

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印度东北部极其潮湿和构造活跃的西隆高原前寒武纪石英岩的微裂缝和化学风化耦合：对原位石英风化和石英粉砂生产的影响

石英粉是最丰富的碎屑颗粒，其来源存在争议。石英粉砂通常被认为是破碎的石英砂，归因于冰川、风积和/或长河流的输送。在本文中，我们重点介绍了前寒武纪石英岩（>92% 石英，含或不含 6%–8% 云母，不含长石）的深层风化剖面 (≤7 m) 中原位石英粉砂的起源，这是一种已知的岩石耐风化，在西隆高原（印度东北部）。该地区是地球上构造最活跃、雨量最多的地区之一。我们首次讨论了详细的现场岩石学和微观结构证据，包括石英中从基岩到腐泥土 (2-3 m) 和结核带 (NZ; ∼0.5 m) 到土壤 (≤2-5米), 在高原通过 3-4 My 的耦合机械-化学过程生产石英粉。石英从基岩石英岩中的中砂（1.13-1.36 Φ）到腐泥土中的细砂（2.55-2.67 Φ）和新西兰（2.12-4.4 Φ）到土壤中的粗和中粉砂（4-5 Φ）的尺寸逐渐减小, 随着粘土矿物的增加 (≤80%)，表征了剖面。与折返和/或地震活动相关的石英岩微裂缝为酸性水攻击和促进石英中的化学风化提供了途径，这反过来又在正反馈回路中影响了微裂缝加宽、孔隙度增强和石英弱化。云母-微生物相互作用促进了流体的酸度，导致铝和铁的流动和更多的粘土矿物生产，并增强了无长石石英岩中原位石英溶解的腐蚀潜力。因此，即使是具有极强抗性的富含石英的岩石的脆性崩解和化学风化也有助于长期的风化层发育和全球石英粉砂的生产。