Detrital zircon U-Pb geochronology, trace-element and Hf isotope geochemistry of the metasedimentary rocks in the Eastern Himalayan syntaxis: Tectonic and paleogeographic implications

The origin of the Greater Himalayan Sequence in the Himalaya and the paleogeographic position of the Lhasa terrane within Gondwanaland remain controversial. In the Eastern Himalayan syntaxis, the basement complexes of the northeastern Indian plate (Namche Barwa Complex) and the South Lhasa terrane (Nyingchi Complex) can be studied to explore these issues. Detrital zircons from the metasedimentary rocks in the Namche Barwa Complex and Nyingchi Complex yield similar U-Pb age spectra, with major age populations of 1.00-1.20 Ga, 1.30-1.45 Ga, 1.50-1.65 Ga and 1.70-1.80 Ga. The maximum depositional ages for their sedimentary protoliths are similar to 1.0 Ga based on the mean ages of the youngest three detrital zircons. Their minimum depositional ages are similar to 477 Ma for the Namche Barwa Complex and similar to 499 Ma for the Nyingchi Complex. Detrital zircons from the Namche Barwa Complex and Nyingchi Complex also display similar trace-element signatures and Hf isotopic composition, indicating that they were derived from common provenance. The trace-element signatures of 1.30-1.45 Ga detrital zircons indicate that the 1.3-1.5 Ga alkalic and mafic rocks belt in the southeastern India is a potential provenance. Most 1.50-1.65 Ga zircons have positive epsilon(Hf)(t) values (+1.2 to +9.0), and most 1.70-1.80 Ga zircons have negative eHf(t) values (-7.1 to -1.9), which are compatible with those of the Paleo- to Mesoproterozoic orthogneisses in the Namche Barwa Complex. Provenance analysis indicates that the southern Indian Shield, South Lhasa terrane and probably Eastern Antarctica were the potential detrital sources. Combined with previous studies, our results suggest that: (1) the Namche Barwa Complex is the northeastern extension of the Greater Himalaya Sequence; (2) the metasedimentary rocks in the Namche Barwa Complex represent distal deposits of the northern Indianmargin relative to the Lesser Himalaya; (3) the South Lhasa terrane was tectonically linked to northern India before the Cambrian. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.