Integrated U–Pb zircon and apatite geochronology of the Phulad Shear Zone, Rajasthan, India: implications for pegmatite emplacement, shear-zone reactivation, and mineralization

The Phulad Shear Zone (PSZ), situated along the western margin of the South Delhi Fold Belt (SDFB), Rajasthan, India, represents a major crustal-scale deformation corridor that records prolonged tectonic, magmatic, and hydrothermal evolution. Despite extensive structural investigations, the timing of magmatism, shear-zone reactivation, and associated mineralization within the PSZ remains poorly understood. This study integrates new LA–ICP–MS U–Pb zircon and apatite geochronology to constrain the temporal evolution of pegmatite emplacement and subsequent fluid-assisted tectonothermal processes within the PSZ. Zircon U–Pb analyses from pegmatitic/granitic rocks yield a concordia age of 815 ± 3 Ma (±18 Ma including systematic uncertainty; n = 51; MSWD = 0.78; p = 0.38), interpreted as the timing of zircon crystallization and emplacement of granitic–pegmatitic magmatism during Neoproterozoic tectonism. In contrast, apatite U–Pb analyses from the same structural domain define a statistically robust lower intercept age of 534.2 ± 5.6 Ma (expanded uncertainty ±13.1 Ma; n = 58; MSWD = 5.2), interpreted as the timing of late-stage tectonothermal resetting induced by fluid circulation and shear-zone reactivation. The combined geochronological data support a two-stage tectono-magmatic–hydrothermal evolution for the PSZ involving (i) emplacement of granitic–pegmatitic melts during Neoproterozoic crustal reworking and (ii) terminal Neoproterozoic–Cambrian fluid-assisted deformation that promoted mineralization along structurally controlled permeability pathways. These findings highlight the importance of crustal-scale shear zones in focusing magma emplacement and subsequent hydrothermal mineralization.