Tethyan suturing in Southeast Asia: Zircon U-Pb and Hf-O isotopic constraints from Myanmar ophiolites

Ophiolites that crop out in Southeast Asia represent the relics of the Tethys Ocean, which existed between the continents of Gondwana and Laurasia during much of the Mesozoic. Two ophiolite belts in Myanmar, i.e., the Eastern Belt and the Western Belt, have been conventionally regarded as parts of a single suture connecting with the Yarlung-Tsangpo suture in the Tibetan Plateau and displaced by the dextral Sagaing fault. Here we present for the first time a combined analysis of zircon secondary ion mass spectrometry U-Pb ages and Hf-O isotopes of two Myanmar ophiolites, the Kalaymyo ophiolite from the Western Belt and the Myitkyina ophiolite from the Eastern Belt. Our results show that the Kalaymyo ophiolite has an Early Cretaceous age (ca. 127 Ma), coeval with Neo-Tethyan ophiolites along the Yarlung-Tsangpo suture. In contrast, the Myitkyina ophiolite was formed during the Middle Jurassic (ca. 173 Ma) and thus the Eastern Belt is the southern continuation of the Meso-Tethyan Bangong-Nujiang suture in the Tibetan Plateau. Consequently, we argue that the two Myanmar ophiolite belts belong to two different sutures of the Meso-Tethys and Neo-Tethys, and that the boundary between the Sibumasu and west Burma blocks is a Jurassic suture rather than a transcurrent shear zone.