Late Cretaceous Intraplate Mafic Dyke Swarms in the East Kunlun Orogen, Northern Tibetan Plateau: Implications for Lithospheric Reactivation and Early Surface Uplift

The Cretaceous represents a key period in the geodynamic evolution of the Tibetan Plateau and the initial development of its paleotopography. While widespread orogenesis and magmatism associated with the Lhasa–Qiangtang collision are well documented in southern Tibet, coeval magmatic records in northern Tibet are extremely limited, hindering constraints on the deep processes responsible for surface uplift. Zircon U–Pb ages, whole-rock geochemistry, and Sr–Nd–Hf isotopes are presented for two mafic dyke swarms from the East Kunlun Orogen, northern Tibet. The two dyke swarms were emplaced at 91.8 ± 2.0 Ma and 84.8 ± 0.6 Ma, indicating a previously underrecognized episode of Late Cretaceous mafic magmatism in northern Tibet. They are subalkaline tholeiites enriched in LILEs and LREEs, depleted in HFSEs, and characterized by negative Nb–Ta anomalies. Their decoupled Nd-Hf isotopes (εNd(t) = −4.96 to +0.94; εHf(t) = +3.75 to +5.76) indicate derivation from an enriched lithospheric mantle metasomatized by slab-related fluids during Permian-Triassic Paleo-Tethyan subduction. Partial melting modeling indicates that the magmas were generated by low-degree (1–5%) decompression melting of lherzolite within the spinel–garnet transition zone. We propose that these mafic dyke swarms formed in an intraplate extensional setting triggered by far-field stresses associated with the Lhasa–Qiangtang collision, which reactivated lithosphere-scale faults and induced localized mantle melting. These results provide new petrological constraints on Late Cretaceous intracontinental extension in northern Tibet and highlight mafic dyke swarms as key probes for linking lithospheric reactivation to early surface uplift of the Tibetan Plateau.