Major, trace element, and SrNd isotopic geochemistry of Cenozoic basalts in Central‐North and East Mongolia: Petrogenesis and tectonic implication

Abstract

This paper presents new major element, trace element, and SrNd isotope data of Cenozoic basalts in volcanic provinces Hovsgol, Taatsiin Gol, and Dariganga‐Abaga in Northern, Central, and Eastern Mongolia, respectively, to explore the petrogenesis of the basalts and their geodynamic setting. Cenozoic volcanic rocks in Mongolia are dominated by basalts, belonging to alkaline and tholeiitic series, and are characterized by ocean island basalts (OIB)‐like major and trace element signature, such as enrichment of light REE relative to heavy REE and enrichment in both large‐ion lithophile elements (LILE) and high‐field‐strength elements (HFSE) with positive NbTa anomalies in primitive mantle‐normalized spider diagram. On the other hand, the Central‐North Mongolian basalts are higher in SiO2 and Al2O3 but lower in MgO, CaO, and TiO2 than East Mongolian basalts and display positive K anomaly, which is in contrast to the negative K anomaly of the latter. Despite the evolved nature of the Central‐North Mongolian basalts, the roles of crustal contamination and fractional crystallization, or assimilation coupled with fractional crystallization (AFC), are insignificant in the genesis of the basalt; instead, both the mantle heterogeneity and melting condition have significant contributions to the compositional variations of the basalts. Importantly, the SrNd isotopic signatures suggest that the mantle sources are characterized by mixing of two isotopic components, a depleted mantle (DM) and an enriched mantle (EM). Although, the EM component is variable, which can be ascribed to metasomatized subcontinent lithosphere (SCLM) and altered recycled oceanic crust (ROC) for the mantle sources of the Central‐North and East Mongolian basalts, respectively. Taking these results together with published age and high‐resolution tomographic data, we propose that all Cenozoic volcanism in Mongolia is related to shallow mantle (asthenosphere) upwelling stemming from the mantle transitional zone (MTZ), but the triggering causes for the mantle upwellings are different. The mantle upwelling related to generation of the Central‐North Mongolian basalts was likely triggered by a far‐field effect of the Indo‐Asian collision, which might have caused the avalanched/subducted materials of the Mongol‐Okhotsk and/or the Central Asian orogenic belt (CAOB) that sink into and stagnated within the MTZ. The mantle upwelling related to the formation of the East Mongolian basalts, which are located at the westernmost of the big mantle wedge constructed by the subducting and stagnant Pacific slab, was induced directly by the westward subduction of the Pacific Plate beneath East Asia.

Melting Dynamics of Late Cretaceous Lamprophyres in Central Asia Suggest a Mechanism to Explain Many Continental Intraplate Basaltic Suite Magmatic Provinces

“…The area in the red box is shown in detail in (b). (b) Sketch map showing the distribution of Cretaceous to Cenozoic mafic magmatism across central and eastern Asia continent (Sheldrick, Barry, et al., 2020; Togtokh et al., 2018). Also shown are the major sutures, faults, basins, and the N‐S trending gravity lineament.…”

“…In detail, the pre‐110 Ma mafic rocks across central and eastern Asia generally have calc‐alkaline compositions with enriched radiogenic isotopes and negative anomalies in Nb and Ta (Gao et al., 2008; Kong et al., 2019; Sheldrick, Hahn, et al., 2020; Zhang et al., 2003), and carry significant contributions from lithospheric mantle (Geng, Liu, et al., 2019; Sheldrick et al., 2018; Zhang et al., 2002). In contrast, their post‐110 Ma counterparts (Figure 1b) are characterized by alkaline compositions with depleted radiogenic isotopes and positive anomalies in Nb and Ta (Meng et al., 2018; Togtokh et al., 2018; Wu, Ling, et al., 2017; Xu et al., 2018), and are sourced directly from the asthenosphere (Barry et al., 2003; Ma et al., 2014; Menzies et al., 1993; Xu et al., 2004). It is still unclear if the coincident transition represents a ubiquitous physicochemical process operating across central and eastern Asia, especially when the sources of mantle melts appear to be so diverse.…”

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

“…Despite few studies of their geochemistry (Barry and Kent, 1998;Yarmolyuk et al, 2015), there is still great controversy on the origin of these basalts. 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). However, it will be difficult to use the BMW model to explain the petrogenesis and geodynamic setting of the basalts in Mongolia, especially those in South Mongolia, since South Mongolia is about 2000 km west of the present Pacific trench, which is too far to correlate the volcanic rocks there to the Pacific subduction.…”

Late Cenozoic Uguumur and Bod-Uul Volcanic Centers in Northern Mongolia: Mineralogy, Geochemistry, and Magma Sources

“…Multiple events of magmatic activity have produced geographically dispersed volcanic fields (Figure 1a), sometimes of controversial origin. Volcanism in the region has received ample literature [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”

“…Multiple events of magmatic activity have produced geographically dispersed volcanic fields (Figure 1a), sometimes of controversial origin. Volcanism in the region has received ample literature [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The available publications discuss Late Cenozoic volcanism in terms of ages, mineralogy, majorand trace-element chemistry, and isotope systematics used to reconstruct the sources of magma and causes of Late Cenozoic volcanic activity in Central Asia.…”