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

Abstract

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 1.00–1.20Ga, 1.30–1.45Ga, 1.50–1.65Ga and 1.70–1.80Ga. The maximum depositional ages for their sedimentary protoliths are ~1.0Ga based on the mean ages of the youngest three detrital zircons. Their minimum depositional ages are ~477Ma for the Namche Barwa Complex and ~499Ma 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 1.30–1.45Ga detrital zircons indicate that the 1.3–1.5Ga alkalic and mafic rocks belt in the southeastern India is a potential provenance. Most 1.50–1.65Ga zircons have positive εHf(t) values (+1.2 to +9.0), and most 1.70–1.80Ga zircons have negative εHf(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 Indian margin relative to the Lesser Himalaya; (3) the South Lhasa terrane was tectonically linked to northern India before the Cambrian.