Tectonic setting and provenance of Early Cretaceous strata in the footwall of Main Central Thrust, Eastern Nepal: Implications for the archipelago palaeogeography of the Neo‐Tethys

The Early Cretaceous palaeogeography prior to the India‐Asia collision is still controversial. There are two end‐member models – an integrated passive margin versus an archipelago. Here, we report zircon U–Pb ages, Hf, and whole‐rock Nd isotopes of newly defined Cretaceous mica schists from the Main Central Thrust to constrain the Early Cretaceous palaeogeography of the Himalaya. The mica schists have Early Cretaceous zircons with εHf(t) values of −21.1 to −9.2. The mica schists are characterized by TDMC values of 1.8–2.5 Ga and whole‐rock εNd(0) value of −24.0. These features imply that these zircons generated from partial melting of lower crust as a result of an extension in some older continental crust, which were transported and deposted to form the protolith of the Cretaceous mica schists. Age pattern comparisons indicate that the age populations of the Cretaceous mica schists are significantly distinct from those of other Cretaceous strata in the Himalaya. It is obvious that the protolith of the Cretaceous mica schists were formed in an independent terrane (Arun) in the Neo‐Tethys with significant tectonic separations proventing any inputs from the Tibetan Himalaya, Greater Himalaya, or Indian Craton since 120 Ma. Combined with published U–Pb ages and other geological data, our data supports the archipelago palaeogeography with rifted terranes in the Neo‐Tethys Ocean, shedding light on the multiple amalgamation events along the India‐Asia collision zone. A new model of the tectonic evolution of the Himalayan orogen at the Early Cretaceous: (a) at 130 Ma, the Mid‐Oceanic Ridges of the Neo‐Tethys approached to subduct into Eurasia, the mantle plume weakened Indian and Australia but extension and motion of plate did not happen, the Arun Microcontinent defined in our study and Tibetan/Greater Himalaya Microcontinent had already isolated from Gondwana Continent; (b) at 120 Ma, the Mid‐Oceanic Ridges had subducted into Eurasia. Subducted oceanic crust initiated the extension and northwestward motion of Arun Microcontinent and Tibetan/Greater Himalaya Microcontinent. Extension generated relevant volcanic rock and sediments in the margin of Arun Microcontinent and Tibetan/Greater Himalaya Microcontinent. Their northwest motions away from Australia had been adjusted by the transform fault along west and northwest of Australia; (c) at 110 Ma, continuous extension made the subsidence of north margin of India and new strata deposited on the Lesser Himalaya. The