期刊
BULLETIN OF VOLCANOLOGY
卷 82, 期 6, 页码 -出版社
SPRINGER
DOI: 10.1007/s00445-020-01381-9
关键词
Ignimbrite; Rheomorphism; Flood basalt; Deccan traps; K; Pg boundary
资金
- post-doctoral Research Associateship of the Council of Scientific and Industrial Research (CSIR), Government of India [09/087(0971)/2019EMR-I]
- CSIR [09/087(0908)/2017-EMR-I]
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.
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