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

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.

Apatite Geochemical and Nd Isotopic Insights into Trachyte Petrogenesis in the Tianchi Volcanic Area of Changbai Mountain, NE China

“…1a), it is also located on the interaction zone between the Pacific subduction zone and Eurasia. Its existence is of great significance for understanding the regional tectonic magmatism and evolution that may be related to the subduction of the Pacific Plate (Zou et al, 2008; (Li et al, 2021;Zhang X B et al, 2021) showing the sampling sites (CBS-13 and CBS-2). JJOB = Jing-Ji orogenic belt; CMVF = Changbai Mountain volcanic field.…”

“…Quaternary intermediate-felsic volcanic rocks in the TVA are widely distributed in the volcanic cone area. According to the zircon U-Pb, K-Ar and 14 C isotopic dating data (Zou et al, 2005;Tang et al, 2007;Wei, 2014;Li et al, 2021), the Tianchi volcano's 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) (Fig. 1b).…”

“…It is also of great scientific significance to clarify the differentiation and formation of magma in the shallow part of the continental crust. At present, petrogeochemistry and limited mineralogical studies show that most of the magma eruption and evolution in the TVA are derived from the differentiation of basaltic magma from the upper mantle associated with plate subduction (Andreeva et al, 2014;Li et al, 2021). Pan et al (2017) believed that the Millennium eruption of Tianchi volcano was triggered by the mixing of trachytic and alkaline rhyolitic magma, which further suggests that the two types of magma came from different source regions.…”

Zircon U–Pb geochronology and geochemistry of the Late Jurassic granite porphyries from central‐eastern Jilin Province, NE China: Petrogenesis and tectonic implications

“…Northeast China is located in the superposition of the EXOB (Long et al, 2020; Tang et al, 2016) and the Pacific tectonic domain (Ganbat et al, 2021; Li, Xu, et al, 2021; Wu et al, 2004; Xu et al, 2020) (Figure 1a,b). During the Late Proterozoic to Late Paleozoic, the region experienced the subduction stage of the Paleo‐Asian Ocean, marked by the accretionary metamorphic complex and the sporadic ophiolite suite formed by the subduction effect (Miao et al, 2007; Wilde et al, 2000).…”

“…In situ Lu-Hf isotope measurements were performed using a Thermo Finnigan Neptune-plus MC-ICP-MS (US, USA) fitted with a J-100 femto-second laser ablation system (Applied Spectra Inc.), housed at the Sun and McDonough (1989); compositions of the lower continental crust are from Rudnick and Gao (2003) NHGETSCL. The analytical procedures and calibration methods are similar to those described by Li, Xu, et al (2021). Zircons were ablated for 31 s at a repetition rate of 8 Hz at 1.5 J/cm 2 , and the ablation pits were et al, 2006) were treated as quality controls.…”