U-Pb zircon ages for Yarlung Tsangpo suture zone ophiolites, southwestern Tibet and their tectonic implications

Abstract

Ophiolite complexes preserved along the Yarlung Tsangpo suture zone (YTSZ) and obducted onto the northern continental margin of India in southern Tibet represent the remnants of the once extensive Permian–Mesozoic Neo-Tethyan Ocean that separated India from Asia. Complete ophiolite successions are preserved near Xigaze, whereas the rest of the belt is essentially represented by mantle rocks with subordinate disrupted lower crustal rocks. U–Pb zircon LA-MC-ICP-MS geochronology on two gabbro samples from the Luobusa ophiolite yielded concordant data with mean 206Pb/238U ages of 149.9 ± 1.4 (2σ) Ma and 150.0 ± 5.0 Ma. These ages are in contrast to a younger age of 131.8 ± 1.0 Ma obtained from a pegmatitic gabbro in Xigaze. Five U–Pb zircon TIMS ages from gabbroic samples in the western portion of the ophiolite belt reveal that the Dangxiong ophiolite formed between 126.7 ± 0.4 Ma and 123.4 ± 0.8 Ma. Zircons from the Jungbwa ophiolite have similar ages of 123.4 ± 0.8 Ma and 123.9 ± 0.9 Ma. A single zircon analysed from a gabbro in Kiogar has an age of 159.7 ± 0.5 Ma. Geochronological data reported here show YTSZ ophiolites formed in association with intra-oceanic subduction zone systems and are related a significant tectonic episode within the Tethyan Ocean during Late Jurassic to Early to mid Cretaceous times.