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The earliest record of Himalayan detritus in the Himalayan foreland and the erosion sequence of different lithotectonic units of the Himalaya are critical for reconstructing collision and crustal deformation of the orogenic belt. In this study, bulk‐rock major, trace and rare earth elements of 19 fine‐grained clastic sedimentary rock samples from Eocene to Pliocene strata of the Bengal Basin were examined to study their provenance and erosion of the Himalaya. Combining with previous detrital zircon age data from the Bengal Basin, Nepal foreland basin, and South Tibet, we suggest that detritus from the uplifted Tethyan Himalayan Sequences and the Gangdese Arc had not been carried into the Himalayan foreland at least before Late Miocene, and that the Bengal Basin was in a passive continental margin setting from Eocene to Early Miocene, receiving detritus from a felsic sedimentary rock source. The earliest Himalayan detritus recorded in the Eocene strata of Bengal Basin were probably derived from the antecedent sedimentary cover of the Greater Himalayan crystalline rocks. We assume that the lack of Cretaceous Gangdese detritus in the Himalayan foreland from Eocene to Middle Miocene is due to a geomorphic barrier between the Tethyan Himalaya and the Himalayan foreland. Detritus from the Greater Himalayan crystalline rocks were first recorded in the Middle–Late Miocene Boka Bil Formation of the Bengal Basin, which is consistent with the uplift and exhumation time of the Greater Himalayan Sequences. [ABSTRACT FROM AUTHOR]

The Bengal Basin is located in the foreland of the eastern Himalaya and records late Palaeocene to Pleistocene sedimentation. This makes the Bengal Basin an ideal place to study the evolution of the eastern Himalaya by provenance researches. Even though there have been several studies about its provenance, a consensus has not been reached about when the Himalayan and Gangdese‐derived detritus started to deposit in the eastern Himalayan foreland. Here, we study the provenance of Eocene to Pleistocene sedimentary successions of the Bengal Basin by detrital zircon U–Pb geochronology and Hf isotope analyses. Detrital zircon U–Pb age spectra show a predominant peak of ~470–580 Ma in all the samples. A peak at this time is prominent in sediments of the Tethyan Himalaya and Lesser Himalaya, which means the detritus eroded from Himalaya may have been deposited in the Bengal Basin after the late Palaeocene‐early Eocene, synchronous with detritus derived from the western and central Himalaya. Gangdese‐derived zircons were firstly recorded in the late Eocene Kopili Formation, and they were sporadic from the late Eocene to middle Miocene, which was probably due to the long distance between the Bengal Basin and the Lhasa Block, to the forebulge in the Lesser Himalayan Sequence, or to a wide tectonic separation at that time. The first influx of abundant Gangdese‐derived zircons occurred in the lower part of the Boka Bil Formation in the late Miocene (~10 Ma), which was probably caused either by the Brahmaputra River capturing the Yarlung Tsangpo River or by a much later terminal collision between India and Eurasia, or both. [ABSTRACT FROM AUTHOR]

The Tethyan Himalaya Sequence between the Yarlung‐Zangbo Suture and South Tibetan Detachment is a fundamental component of the Himalayan orogenic belt, traditionally considered to belong to the passive continental margin of India. However, the eastern Tethyan Himalaya Sequence is poorly understood, compared with that in the central and western Himalaya. To improve general understanding, we undertook north‐south geological‐structural profiles across all the litho‐tectonic units of the eastern Tethyan Himalaya Sequence and produced new isotopic‐geochemical data from all units, to constrain their mode of occurrence, structure, tectonic setting, and time of formation. The whole Tethyan Himalaya Sequence consists of a thrust‐imbricated mélange that contains blocks of ophiolites (such as Lang County, Yumen, and Lhunze), oceanic islands (e.g., Comei) with ocean island basalts‐type basalts, mafic greenschists, limestone olistoliths, and cherts in a turbiditic matrix of greywackes, siltstones, and slates in south‐directed thrust slices. Our findings suggest that the eastern Tethyan Himalaya Sequence represents the evolution of an accretionary prism, rather than a passive margin of the Indian Plate. The prism was created during northward subduction of Neo‐Tethys between ~130 and ~50 Ma. These data allow us to produce a new tectonic model for the structural development of the eastern Himalayan orogenic belt in relation to the India‐Asia collision. [ABSTRACT FROM AUTHOR]