U-Pb Zircon Geochronology and Trace-Element Geochemistry of Attabad Lake and Nomal Village Granitoids from the Karakoram and Kohistan Batholiths, NW Pakistan: Local Constraints on Magmatic Evolution

The timing and nature of the tectonic transition from Neo-Tethyan subduction to India-Asia collision along the NW Himalaya remain debated, particularly regarding the relationship between continental arc and post-collisional magmatism in the Karakoram and Kohistan batholiths. We present zircon U-Pb ages, whole-rock geochemistry, and zircon trace-element data from three granitoid samples from the Attabad Lake area (Karakoram Batholith) and the Nomal area (Kohistan Batholith). Zircon U-Pb dating yields crystallization ages of 103.4 ± 1.7 Ma for the Karakoram diorite, and 46.10 ± 0.79 Ma and 43.59 ± 0.88 Ma for the Kohistan enclave and host quartz monzonite, respectively. The Karakoram diorite shows LREE enrichment [(La/Yb)N = 5.93–78.52] and positive zircon Ce anomalies (Ce/Ce* = 9.00–18.70), features broadly consistent with crystallization from an oxidized, subduction-related magma. In contrast, the Kohistan quartz monzonite exhibits elevated SiO2 (65.01–66.35 wt%), low Mg# (25.9–27.2), and a flat to slightly negative Eu anomaly (Eu/Eu* = 0.94), which may reflect crustal melting during post-collisional extension. The enclave displays mantle-like signatures with high Sr (1623 ppm) and a positive Eu anomaly (Eu/Eu* = 1.14), suggesting a mafic recharge event. Zircon Th/U ratios (>0.1) and magmatic REE patterns support a magmatic origin for the dated zircons. These results are compatible with, but do not independently establish, previously proposed regional models. They provide additional local constraints that point to spatially heterogeneous magmatic evolution along the NW Himalayan syntaxis, with continental arc magmatism in the Attabad Lake area during the mid-Cretaceous and a transition to post-collisional extension in the Nomal area during the Eocene.