Synchronous Cretaceous magmatism and migmatization in the Lohit and Dibang valleys, easternmost Himalaya

Subduction of the Neo-Tethys Oceanic lithosphere triggered significant Mesozoic arc magmatism and migmatization along the Himalayan arc. However, the processes and timing of these events in the eastern Himalayas have not been well studied. We provide geochemical and zircon U–Pb geochronological data on granitoids and migmatites from the Lohit Plutonic Complex (LPC) exposed in the easternmost Himalayas. This complex includes gabbro, diorite, granodiorite and migmatite, with evolved granites. The LPC granitoids in the Lohit Valley crystallized from ∼105 to 63.8 Ma, while this range in the Dibang Valley is from ∼154.13 to 73.91 Ma. These granitoids are metaluminous (I-type), calc-alkaline and enriched in large ion lithophile elements with negative Nb anomalies, indicating their subduction-related origin. Trace and rare earth element modelling suggest granite formation through partial melting of the depleted mantle in spinel lherzolite facies. The geochronological results provide, for the first time, the timing of migmatization within the LPC from ∼88 to 69 Ma, i.e. prior to India–Asia collision. This event of migmatization was synchronous with the subduction-related magmatism. The melanosome and leucosome are metaluminous, with the leucosome showing peritectic hornblende-bearing garnet, K-feldspar, plagioclase, quartz and biotite inclusions, formed through water-fluxed partial melting of hydrous calc-alkaline arc-related igneous rocks.