Geothermal He and CO2 variations at Changbaishan intra-plate volcano (NE China) and the nature of the sub-continental lithospheric mantle

We report new He and CO2 data for geothermal fluids from Changbaishan Volcano located on the border of China and North Korea. Helium isotope ratios reach a maximum of 5.4 R-A (where R-A = He-3/He-4 in air) whereas carbon isotope values (delta C-13) fall between -2 and -7%(vs. PDB). The ratio of CO2/He-3 varies between 0.5-7.1 (x 10(9)) for gas samples but is considerably higher (similar to 10(12)) in waters. The combined He-CO2 systematics reveal the clear imprint of a dominant subducted slab contribution to the total CO2 inventory. We conclude that these geothermal volatiles originate from the sub-continental lithospheric mantle (SCLM) in NE China and represent ancient fluids captured by prior metasomatic events. Citation: Hahm, D., D. R. Hilton, M. Cho, H. Wei, and K.-R. Kim (2008), Geothermal He and CO2 variations at Changbaishan intra-plate volcano (NE China) and the nature of the sub-continental lithospheric mantle, Geophys. Res. Lett., 35, L22304, doi:10.1029/2008GL035955.