Geochronology and Petrogenesis of Early Pleistocene Dikes in the Changbai Mountain Volcanic Field (NE China) Based on Geochemistry and Sr-Nd-Pb-Hf Isotopic Compositions

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 shieldforming
stage (2.8–0.3Ma), the Tianchi cone construction stage (1.5–0.01Ma), and a calderaforming
stage (0.2Ma-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 1.19–1.20Ma (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 compatiblewith anOIB-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.