Abstract
Changbai Mountains intraplate volcanism (NE China) developed above the 500 km deep stagnant portion of the Pacific slab in the last 20 Ma. The more recent activity includes a shield-forming stage (2.8–0.3 Ma), the Tianchi cone construction stage (1.5–0.01 Ma), and a caldera-forming stage (0.2 Ma-present). Detailed studies on the petrogenesis of the volcanic products between the first two stages and the possible role of geodynamics and local tectonics in controlling the volcanism, however, are lacking. Here, we present structural and whole-rock geochemical and zircon Hf isotopic data on Pleistocene dikes of the Changbai Mountains at the transition from the shield-forming to the Tianchi stage with the aim to constrain their age and the source(s) of their parental magma. The dikes represent the shallower feeding system of monogenetic cones and have a NW-SE strike, which is also the preferred strike of the major fault affecting the area and along which the Changbai Mountains monogenetic scoria cones align. The dikes have a potassic affinity and a trachybasaltic composition. Their zircon U–Pb age is 1.19–1.20 Ma (Calabrian). The trachybasalts are enriched in Rb, Ba, Th, U, Nb, Ta, K, Pb, and LREE and slightly depleted in Sr, Zr, Hf, Ti, and HREE with a weak negative Eu/Eu* (δEu = 0.96–0.97). Trace elements and isotopic compositions are compatible with an OIB-type source with an EMI signature. The calculated (87Sr/86Sr)i(=0.705165–0.705324), (143Nd/144Nd)i(= 0.512552–0.512607, εNd(t) = −0.58 to −1.65), and Hf model ages (TDM2) of 1768–1562 Ma suggest that the trachybasaltic dikes were contaminated by a Mesoproterozoic, relatively basic lower crust. The source of the Calabrian trachybasalts consists of asthenospheric melts modified by a subcontinental lithospheric mantle. These melts upwell from depth and stop at the crust-mantle interface where underplating processes favor the assimilation of ancient lower crust material. During the ascent to the surface along deep-seated crustal discontinuities, these magmas weakly differentiate.
Highlights
The eastern China block includes the eastern margin of the Central Asian orogenic belt, the North China Craton (NCC), the Sulu-Dabie high pressure orogeny belt, the Yangtze Craton, and the southeast coastal orogenic belt of China, and it is characterized by Mesozoic volcanic and intrusive rocks (Figure 1A)
The origin of the Pleistocene magmatism is still debated and different hypotheses have been proposed: 1) low degrees of partial melting of the asthenospheric mantle (Xu, et al, 2020a) possibly contaminated by the addition of crustal material (Sun et al, 2015); 2) partial melting of the subducted slab (Ma et al, 2015); 3) involvement of DM and EM1 end-members (Basu et al, 1991) or OIB and EM1 end-members (Xu et al, 2012); 4) an asthenospheric source metasomatized by recycled subducted silicate sediments or a subcontinental lithospheric mantle (EM1-like) and by carbonated eclogites with a MORB signature (Choi et al, 2020); and 5) an EM1-like source originated from the contamination of an OIB asthenospheric mantle by Paleoproterozoic lithosphere (Lee et al, 2021)
Questions regarding the nature of the mantle and possible crustal sources of the Changbaishan Mountain volcanism and of the dynamics of the Pacific plate subduction remain open
Summary
The eastern China block includes the eastern margin of the Central Asian orogenic belt (the Xing’an-Mongolia orogenic belt), the North China Craton (NCC), the Sulu-Dabie high pressure orogeny belt, the Yangtze Craton, and the southeast coastal orogenic belt of China, and it is characterized by Mesozoic volcanic and intrusive rocks (Figure 1A). The later Cenozoic volcanic rocks mainly consist of basalts emitted in an intraplate setting (e.g., Wu et al, 2011; Zhang and Luo, 2011; Deng et al, 2017) associated to metallogenic and hydrothermal deposits (Sun et al, 2012, 2013; Deng et al, 2017). Changbai Mountains, which consist of basaltic shields, monogenetic vents, and central-type volcanoes, are located above the 500 km deep stagnant slab of the westward subducting Pacific plate (Figure 1A). Three main geodynamic models have been suggested to explain the Changbai Mountain volcanism: an upwelling mantle plume (Mao et al, 1999), an intraplate continental rifting (Gilder et al, 1991), and the Pacific plate subduction New data and constraints on the relative role of the asthenosphere, ancient crust, and stagnant slab in the evolution of intraplate volcanism are provided
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