U-Pb Basement and Detrital Zircon Geochronology of the Southern Tibetan Plateau and Tethyan Himalaya

U-Pb ages of >3500 zircons from basement and Ordovician–Triassic detrital samples from the Lhasa terrane, Qiangtang terrane, and Tethyan-Himalaya provide new constraints on the pre-Mesozoic geological framework and paleogeography of the Neo-Tethys and Tibetan terranes. 1) Carboniferous–Permian strata exposed to the north and south of the E–W trending high-pressure central Qiangtang metamorphic belt (QMB) show no obvious differences in their detrital zircon age probability spectra. These results, together with stratigraphic and sedimentologic similarities, refute previous suggestions that the QMB separates strata of Cathaysian affinity in the north from that of Gondwana affinity in the south. 2) Upper Paleozoic strata with maximum depositional ages of ~540 Ma in the southern Qiangtang terrane are exposed structurally above kyanite/sillimanite-bearing orthogneisses with crystallization ages in the 470–480 Ma range. 3) ~509 Ma granitic basement exposed in the central Lhasa terrane is unconformably overlain by a continuous section of Cambrian through Permian strata. 4) Detrital zircon age probability spectra determined for Ordovician–Triassic strata of Lhasa terrane are distinct from those of Qiangtang strata, but strikingly similar to Tethyan strata of the Tibetan Himalaya. Age probability spectra for Tethyan Himalayan and Lhasa terrane strata have substantial peaks at ~520 Ma and several significant peaks ranging from ~800–1200 Ma and less significant peaks from ~1600–1800 Ma and ~2400–2900 Ma. In contrast the Qiangtang terrane yielded a significant probability peak at ~220 Ma and peaks ranging from ~500–600 Ma, ~750–1050 Ma, ~1800–2000 Ma, and ~2400–2600Ma. These results are unexpected as most tectonic models for the Himalayan–Tibetan orogen suggest the Lhasa and Qiangtang terranes were separated by a relatively narrow and short-lived Meso-Tethys Ocean whereas the Lhasa terrane and Tethyan Himalaya were separated by a wide and long-lived Neo-Tethys Ocean.