Search

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. Research highlights: First report of pillow structures from North Delhi Fold Belt. Identification of mafic- ultramafic association and possibility of an ophiolite setting. [ABSTRACT FROM AUTHOR]

The Palaeoproterozoic Aravalli Supergroup in Salumber region includes a basal unit of metabasic volcanic rocks (Salumber volcanic rocks) overlain by a volcaniclastic/conglomerate one. Although these volcanic rocks have been metamorphosed to green-schist facies, some primary volcanic features are still preserved. This metabasic volcanic sequence can be further differentiated on the basis of textural variations, and the mineral assemblages are: (a) oligoclase + actinolite + chlorite + epidote; and (b) oligoclase + hornblende+ chlorite + biotite + Fe-Ti oxides. The SiO2 content ranges from ∼47.7 to 55.8% and MgO from ∼4.2 to 12.8%. Geochemical characteristics allow their subdivision into high Mg and Fe tholeiites. Inverse relationship of MgO with silica, alkalis and Zr is generally consistent with fractionation mechanism, also suggested by a change in colour of the rocks from dark greenish to light greenish towards the upper parts of the sequence. These metabasic volcanic rocks are enriched in incompatible trace elements and LREE (La = 30 − 40 × chondrite, Lu = 2 − 5 × chondrite), and demonstrate affinity mainly with MORB and within plate settings in geochemical tectonic discrimination schemes. The geochemical characteristics suggest a complex evolutionary history envisaging derivation of the melt from an enriched heterogeneous lithospheric source. [ABSTRACT FROM AUTHOR]