Decoding the tectonomagmatic evolution of the Ladakh Magmatic Arc, NW Himalaya: A multi-proxy geochemical and isotopic approach

Magmatic arcs are the active locus of crustal formation, and their knowledge of spatiotemporal geochemical variation is vital for understanding the evolution of collisional systems. Here, we compare geochemical and isotopic results from the precollisional Dras-Nidar Island Arc Complex (DNIAC), pre- to syn-collisional Ladakh Batholith (LB) that formed the part of the well-known Kohistan-Ladakh Batholith, and post-collisional mafic dykes. It is observed that the long-term magmatic evolution was controlled by the Neo-Tethyan Ocean geodynamics. The Ladakh magmatic arc records three distinct magmatic stages through its geochemical and isotopic evolution. The pre-collisional DNIAC (160-110 Ma) shows tholeiitic to calc-alkaline melts with depleted mantle signatures (ε_Nd > +5 and ⁸⁷Sr/⁸⁶Sr < 0.704), transitional to syn-collisional LB granitoids and associated Khardung volcanics (103-45 Ma) reflecting enriched signatures (ε_Nd +2 to -4, ⁸⁷Sr/⁸⁶Sr = 0.704-0.708, La/Sm > 3, Th/La > 0.2) due to sediment subduction and crustal assimilation. While post-collisional mafic dykes (< 45 Ma) reflect lithospheric mantle metasomatism (enriching incompatible trace elements including rare earth elements) with limited crustal interaction (ε_Nd +1 to +3). This demonstrates a progressive evolution from a fluid-dominated mantle wedge melting to a sediment-driven crustal influence and finally to an enriched mantle melting, highlighting the critical role of slab dynamics and crustal recycling in continental growth during arc-continent collision. Thus, we concluded that the contribution from the sediment subduction is more pronounced in the KLB compared to the DNIAC.