Evidence for long-lived continental intraplate magmatism: A case study from Mongolia

The closure of the Mongol-Okhotsk Ocean in Jurassic – Cretaceous times led to the final amalgamation of the interior of Eastern Asia, thus placing Mongolia in an intraplate tectonic setting. Small and widespread volcanic fields of Mesozoic and Cenozoic age are known through Eastern Asia, attributed to both post-collisional and intraplate mechanisms. In Mongolia, intraplate volcanic fields are scattered across the central and eastern parts of the country. Although several models have been proposed to explain the origin of this late Mesozoic – Cenozoic intraplate magmatism in Mongolia, there is still on-going debate about the process(es) that lead to it. Moreover, there are no temporal reconstructions on the extent of post-collisional magmatism in the area preceding intraplate magmatic activity, nor any hypotheses on the timing of the onset of the latter. In this study, we differentiate between post-collisional and intraplate magmatism in Mongolia using a set of geochemical, isotopic, palaeomagnetic and zircon data, and define the onset of intraplate magmatic activity at 107 Ma. Through evaluation of nearly 700 published radiometric data from the various volcanic fields across Mongolia along with newly-obtained age constraints, we reveal a complex temporal and spatial evolution of the magmatism that runs parallel in different volcanic fields through time, and we identify the extent of hiatuses in the magmatic activity. Based on the assessed data we discuss the source of bias in our understanding of the magmatic history of Mongolia and evaluate the various proposed models for the origin of the Mongolian magmatism. Finally, we suggest that asthenospheric upwellings were induced through a delamination event beneath Mongolia in the late Mesozoic. This initiated the intraplate magmatism, the temporal evolution of which is prolonged due to enhanced mantle flow related to northward progression of Tethys and the Indian plate.