Zircon isotope–trace element compositions track Paleozoic–Mesozoic slab dynamics and terrane accretion in Southeast Asia

Abstract

Variation in zircon trace element (TE) and isotopic composition data have been used to infer changes in global-scale processes; however, few studies have explored zircon TE data as a comprehensive means to track regional shifts in tectonic regimes. In this contribution, we explore the utility of zircon TE data to record the well-documented Late Paleozoic–Mesozoic tectonic history in Southeast Asia, which includes transitions from continental magmatism to island-arc extension, subsequent compression and island-arc accretion, and finally continental collision. We present new U-Pb ages, along with Lu-Hf isotopic and TE data, from 2,478 detrital zircon grains extracted from 17 modern river sediment samples collected across two major suture zones in Thailand. Our results show that zircon Th/U and Nb/Ta mean values increase after ∼300Ma, whereas the percentage of classified ‘felsic’ zircon decline corresponding with the initiation of Nan back-arc basin extension and isolation of the Sukhothai Arc from Indochina. From ∼255 to 235 Ma, zircon εHf(t), LREE/HREE, (Eu/Eu*)N, (Ce/Ce*)N, Nb/Ta, and Th/U mean values decline, whereas Dy/Yb, U/Yb, and the proportion of classified S-type and ‘felsic’ zircon increase, showing the transition from I-type to S-type, and from more juvenile to more evolved magmatism. This transition reflects a shift from arc extension to compression via the closure of the Nan back-arc basin and the collision of the Sukhothai Arc with western Indochina, and the subsequent collision of Sibumasu with the Sukhothai Arc demarking the regional closure of the Paleo-Tethys ocean. Our data also show linear correlations between εHf(t)-DM and trace elemental data, particularly (Eu/Eu*)N, that reflect increasing sediment contamination within the melts. Lastly, our data illustrate that the Sibumasu–Sukhothai Arc collided ∼20 million years earlier in Thailand than in the Malay Peninsula, demonstrating along-strike diachroneity in Paleo-Tethys closure. Thus, time-integrated detrital zircon TE data may reliably track subduction slab dynamics and tectonic evolution beyond U-Pb and Hf isotope data alone.