Geochemical comparison of late Mesozoic and early Cenozoic volcanic rocks in South Mongolia

Abstract

The Mesozoic-Cenozoic volcanic rocks are widely distributed in the interior of the East Asia and document the tectonic transition of East Asia. We present new geochronology and geochemistry data of late Cretaceous-early Cenozoic basalts in Bayantsagaan and Han-Uul volcanic provinces in South Mongolia, in order to explore their petrogenesis and geodynamic settings. The volcanic rocks in the Bayantsagaan and Han-Uul field yielded K-Ar ages of 90.55±1.93 Ma and 55.49±1.49 Ma, respectively. The volcanic rocks in South Mongolia subdivided into to alkaline basalts and tholeiitic series, and are characterized by ocean island basalts (OIB) trace elements features, such as enrichment of light REE relative to heavy REE and enrichment in large ion lithophile elements (LILE). Compared with the late Cretaceous, the early Cenozoic basalts show an increase of Nb and Ta. Crustal contamination and fractional crystallization are insignificant in the genesis of late Cretaceous and early Cenozoic basalts South Mongolia. The available Sr-Nd isotope results indicate that late Cretaceous volcanic rocks, which derived from magmas from the of metasomatized subcontinent lithospheric mantle, whereas the early Cenozoic basalts is ascribed to contributions from the asthenospheric mantle. We propose that the generation of the late Cretaceous volcanic rocks (114-90 Ma) related back arc-extension induced by slab rollback of the westward-subducted Pacific Plate and the subduction zone retreat. Whereas Early Cenozoic volcanism in Mongolia is related to the shallow mantle upwelling (asthenosphere) induced by the edge convection along the northern margin of the North China Craton (NCC), triggered by a far-field effect of Indo-Asian collision.

Tectonic evolution of a sequence of related late Permian transtensive coal-bearing sub-basins, Mongolia: A global wrench tectonics portrait

“…The circular shape of the anomaly belt, and the fact that it crosses the boundaries of tectonic terranes, excludes the possibility that it originates from a surface basin. Moreover, this apparently superimposed anomaly includes a major part of the Khangai Dome -a distinct topographic high in central western Mongolia within which numerous, but volumetrically small, late Miocene to Quaternary volcanic cones and lava flows are spread (Hunt et al, 2012;Ivanov et al, 2015;Khasmaral et al, 2019). The basement of the dome consists of Precambrian gneisses and schists overlain by thick middle Palaeozoic turbidite sequences which are intruded by Permian granitoids (Badarch et al, 2002).…”