Subaerial to subaqueous volcaniclastics from the Bayana sub-basin, North Delhi Fold Belt (NDFB), India: Evidence for a Paleoproterozoic subduction margin

The Paleoproterozoic Jahaj–Govindpura Formation of the Raialo Group of Delhi supergroup, India exposes volcanic and volcaniclastics rock at multiple stratigraphic levels and hence, provides a unique scope for the study of volcaniclastics of varying rheology and their bearing on the tectono-magmatic setting of the basin. From a detailed field study in three spatially disparate sections, associated sedimentary facies types and textural evidences such as clast annealing, deformation in pumice fragments, eutaxitic foliation and shattered crystals, the volcaniclastics are documented as pyroclastic flow (VLC 1), welded tuff (VLC 2), clast-/matrix-supported boulder pyroclastic conglomerate (VLC 3), and pyroclastic fall deposits (VLC 4). Whereas, VLC 1 and VLC 2 are identified as subaqueous, VLC 3 and VLC 4 are grouped under subaerial categories. The facies distribution of volcaniclastics and eastward paleocurrent motif from associated sedimentary facies is indicative of proximal-distal relationship varying between subaerial to sub-marine depositional settings. From collation and comparison of available geochemical data (major, trace element, and REE) of volcanic rock and new geochemical data generated from volcaniclastics under the present study, it is inferred that the source magma was more basic (low SiO 2 and high MgO) resembling tholeiitic to calc-alkaline island-arc source composition while a more intermediate to felsic composition is posited for the volcaniclastics. Considering the ca-1876 Ma time frame of the basin and a subduction-related magmatic character for the volcaniclastics, a possible Orosirian subduction margin, related to the ‘Columbia’ supercontinent, in the vicinity of the Bayana sub-basin in North Delhi fold belt is suggested. Highlights: Primary subaerial to subaquous volcaniclastics described from Paleoproterozoic Bayana sub-basin, North Delhi Fold Belt, India. Unequivocal petrological features allowed subaerial and subaquous emplacement of volcaniclastics. Depending on associated sedimentary facies and paleocurrent motif a proximal-distal relationship established between different volcaniclastic facies. Whereas volcanics register tholeiitic to calc-alkaline composition, a more intermediate to felsic composition is inferred for the volcaniclastics. From geochemical signature, an overall compressional tectonic set-up is suggested with riftogenic Bayana basin a part of it. It is argued that in terms of tectonic and depositional setting, the B