Hydrothermal He and CO2 at Wudalianchi intra-plate volcano, NE China

Chemical and isotopic compositions have been measured for CO2-rich bubbling gases discharging from cold springs in Wudalianchi intra-plate volcanic area, NE China. Observed 3He/4He ratios (2–3 RA) and δ13C values of CO2 (−5‰ to −3‰) indicate the occurrence of a mantle component released and transferred to the surface by the Cenozoic extension-related magmatic activities. The CO2/3He ratios are in wide range of (0.4–97 × 109). Based on the apparent mixing trend in a 3He/4He and δ13C of CO2 diagram from all published data, the extracted magmatic end-member in the Wudalianchi Volcano has 3He/4He, δ13C and CO2/3He value of ∼3.2 RA, ∼−4.6‰ and ∼6 × 1010, respectively. These values suggest that the volatiles originate from the sub-continental lithospheric mantle (SCLM) in NE China and represent ancient fluids captured by prior metasomatic events, as revealed by geothermal He and CO2 from the adjacent Changbaishan volcanic area.

► We measured C and He abundances and isotopes of hydrothermal gas from Wudalianchi, NE China.
► Magmatic compositions indicate ancient subduction zone fluids trapped in the SCLM since the Mesozoic.
► Hydrothermal gases can be used to assess the geochemical feature of SCLM.
► Large variations of mantle enrichment represent heterogeneity of the SCLM beneath the NE China.