Helium and carbon isotopes in the hot springs of Changbaishan Volcano, northeastern China: A material connection between Changbaishan Volcano and the west Pacific plate?

Abstract

Changbaishan Volcano is located in northeastern China, approximately 1400km west of the west Pacific subduction zone. Although the west Pacific plate and Changbaishan Volcano are spatially associated with each other, no previous evidence has demonstrated the existence of a direct material connection between the two. In this study, we utilize helium (3He/4He, CO2/3He) and carbon isotopes (δ13C) from the hot springs of Changbaishan Volcano to exclude the possibility of a direct material connection between the volcano and the west Pacific plate at source. A total of 22 gas samples were collected from three hot springs at Changbaishan Volcano in 2002, 2006, 2014 and 2015; isotopic and geochemical analyses were performed on these samples to trace the possible sources of these gases.Our analysis reveals that values for air-corrected 3He/4He ratios range from 3.98 RA to 6.03 RA (where RA represents the atmospheric 3He/4He ratio), CO2/3He ratios vary from 2.20×108 to 1.92×1011, and δ13C values vary from −7.9‰ to −1.6‰. By comparing these measured values to those of typical mantle and crustal sources, we can infer that hot spring gases from Changbaishan Volcano are mostly characterized by inputs from two isotopically distinct sources: deep mantle fluids and shallower, slab-derived fluids. Fluids liberated from the shallower magma chamber are likely to include ancient Izanagi subduction zone fluids, whereas fluids originating from deeper magma chamber likely consist of MORB-like asthenospheric mantle fluids. Based on these results, we suggest that helium and carbon isotopes in hot springs demonstrate the absence of a direct material connection between Changbaishan Volcano and the west Pacific plate.