The rocks of Raialo Group in the Alwar sub-basin of North Delhi Fold Belt were investigated with a focus on meta-basic lava flows of the Tehla Formation. The basaltic rocks, now occurring as amphibolites, are medium- to fine-grained and show evidence of greenschist to lower amphibolite facies metamorphism, characterized by dominant plagioclase, hornblende, actinolite, chlorite, and minor, epidote, opaque, and Fe–Ti oxide mineral assemblage. The presence of amygdules and vesicles, well preserved primary igneous texture, and relict pyroxenes, at places, confirm their basaltic lineage. In a single outcrop, located to the northeast of Tehla village, well-preserved pillow structures have been discovered. The pillow structures vary in size (few cm to >1 m) and shape (spheroid, elongate and kidney-shaped), and inter-pillow spaces are filled up with chert, at places. This is the first report of pillow basalt occurrence from the North Delhi Fold Belt. In addition to offering evidence of submarine basaltic volcanism, the mega-pillows, gabbroic lenses, and presence of ultramafic rocks in the region suggest a possible ophiolite setting that needs a detailed petrographic and geochemical evaluation.
$\bullet$ First report of pillow structures from North Delhi Fold Belt.
$\bullet$ Identification of mafic- ultramafic association and possibility of an ophiolite setting.
Volume 131, 2022
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