The physical volcanology of widespread rhyolites and dacites overlying flood basalt lavas in the northwestern and northern parts of the 65.5-Ma Deccan Traps, India, is poorly known. We show that these are not lava flows but high-grade (welded and rheomorphic) to extremely high-grade (lava-like) ignimbrites deposited by pyroclastic density currents. Evidence for this interpretation includes the following: (i) flat, planar contacts with the underlying basalts and absence of basal brecciated zones; (ii) pervasive millimeter-to-centimeter-scale flow banding; (iii) parataxitic textures indicating very high degrees of compaction and welding; (iv) strong rheomorphic deformation, producing folds of diverse geometries and sizes showing overprinting relationships, with common tight-isoclinal and sheath (eye) folds that are sometimes refolded into F 2 and even F 3 folds; (v) curvilinear fold hinges with elongation lineations varying from transverse to subparallel to the fold axes; (vi) local boudinage and autobrecciation in flow-banded glassy tuffs; (vii) common and abundant spherulites and lithophysae; (viii) intimate association of tuff and vitrophyre at millimeter to tens-of-meter scales; and (ix) vitroclastic textures showing highly flattened and stretched glass shards and pumice fiamme wrapping around phenocrysts. Whereas rheomorphic and lava-like ignimbrites dominate, some non-welded and welded (eutaxitic) ignimbrites also occur. Voluminous rhyolites and dacites in many flood basalt provinces of the world are recognized as high-grade to extremely high-grade ignimbrites, and the Deccan is no exception. This Deccan explosive silicic volcanism may have significantly contributed to the K/Pg boundary mass extinctions, if contemporaneity can be established by future geochronological work.

中文翻译：

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德干圈闭西北部和北部泛滥玄武岩上广泛分布的流变和熔岩状硅质熔岩

印度 65.5 Ma 德干圈闭的西北部和北部覆盖在泛滥玄武岩熔岩上的广泛流纹岩和英安岩的物理火山学鲜为人知。我们表明，这些不是熔岩流，而是由火山碎屑密度流沉积的高品位（焊接和流变）到极高品位（熔岩状）的熔凝体。这种解释的证据包括以下内容： (i) 与下伏玄武岩平坦、平面接触且没有基底角砾岩带；(ii) 无处不在的毫米到厘米级流量带；(iii) 显示非常高的压实度和熔接度的并列结构；(iv) 强烈的流变变形，产生不同几何形状和尺寸的褶皱，显示叠印关​​系，具有常见的紧等斜和鞘（眼）褶皱，有时会重新折叠成 F 2 甚至 F 3 褶皱；(v) 曲线折叠铰链，其伸长线从横向到平行于折叠轴不等；(vi) 流动带状玻璃凝灰岩中的局部布丁和自碎屑；(vii) 常见且丰富的球晶和石泡；(viii) 凝灰岩和玻璃岩在毫米到几十米尺度上的密切联系；(ix) 玻璃碎屑纹理显示高度扁平和拉伸的玻璃碎片和包裹在斑晶周围的浮石纤维。虽然流变和熔岩状凝灰岩占主导地位，但也出现了一些非焊接和焊接（共生）凝灰岩。世界上许多溢流玄武岩省份的大量流纹岩和英安岩被认为是高品位至极高品位的熔凝岩，德干也不例外。