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

Anaad Chimedtseren,Baatar Munkhtsengel,Bars Amarjargal,Laicheng Miao,Togtokh Khasmaral

doi:10.5564/mgs.v0i49.1223

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 can be 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) with positive K anomaly. Compared with the late Cretaceous, the early Cenozoic basalts show a decrease in the contents of HREE and an increase of Nb and Ta. Crustal contamination and fractional crystallization are insignificant in the genesis of late Cretaceous-early Cenozoic basalts South Mongolia. The available Sr-Nd isotope results indicate that a mixing depleted (DM) and enriched mantle (EM) signature characterize in late Cretaceous volcanic rocks, which derived from magmas from the asthenosphere with some contributions of metasomatized subcontinent lithospheric mantle, whereas the early Cenozoic basalts are ascribed to contributions from the asthenospheric mantle. We propose that the generation of the late Cretaceous-early Cenozoic volcanism (90-40 Ma) in Mongolia is probably 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.

Highlights

The volcanic rocks of Mesozoic-Cenozoic age are distributed over a vast region from the coastal area of East Asia continent and in the interior of the East Asia continent, such as Mongolia as well.Mesozoic volcanism in Mongolia is mainly emplaced during the late Jurassic-early Cretaceous, and late Cretaceous volcanism was mainly distributed in East Mongolia and South Mongolia
It is noted that the “Big Mantle Wedge” (BMW) model has been widely accepted in interpreting the geodynamic setting of the Cenozoic volcanism in East Mongolia and East China (e.g., Zhao et al, 2009; Kuritani et al, 2011; Togtokh et al, 2018; Xu et al, 2012; Zhang et al, 2014; Xu and Zheng et al, 2017)
Some researchers (Barry et al, 2003) believe that ocean island basalts (OIB)-like late Cretaceous- Early Cenozoic basalts in South Mongolia have the same origin as late Cenozoic volcanic rocks in Central Mongolia

Summary

Introduction

The volcanic rocks of Mesozoic-Cenozoic age are distributed over a vast region from the coastal area of East Asia continent and in the interior of the East Asia continent, such as Mongolia as well.Mesozoic volcanism in Mongolia is mainly emplaced during the late Jurassic-early Cretaceous, and late Cretaceous volcanism was mainly distributed in East Mongolia and South Mongolia. Mongolia, demonstrated that bimodal series arc type volcanic rocks migrates from west to east with time. Their origin was linked to the backarc extension induced by slab rollback of the westward-subducted Pacific Plate (Dash et al, 2013; Bars et al, 2018). Some researchers (Barry et al, 2003) believe that OIB-like late Cretaceous- Early Cenozoic basalts in South Mongolia have the same origin as late Cenozoic volcanic rocks in Central Mongolia. We present new geochemical and geochronological data of the Cretaceous -early Cenozoic basalts in South Mongolia Using these results, together with previously published data, we explore the petrogenesis and discuss the geodynamic setting in which the late Cretaceous- early Cenozoic volcanism occurred in South Mongolia

Methods

Results

Conclusion