Abstract:

The Northeast China region, characterized by multiple episodes of tectonic-magmatic activities and complex sedimentary-metamorphic rock assemblages, offers favorable geological conditions for the formation of helium source rocks. However, the distribution patterns and helium generation potential of these rocks have not been systematically revealed. Based on U and Th content tests (ICP-MS method) and chronological analysis of 188 rock samples, this study systematically elucidates the lithological and temporal characteristics of helium source rocks in Northeast China, and constructs a comprehensive evaluation method. The results indicate that: Lithology exerts significant control over helium potential, with acid magmatic rocks (w(U)=7.2×10-6, w(Th)=18.5×10-6), mudstone (w(U)=6.5×10-6, w(Th)=20.5×10-6), and metamorphic rocks derived from argillaceous or granitic protoliths (w(U)=6.8×10-6, w(Th)=15.2×10-6) serving as high-quality helium source rocks due to their enrichment in radioactive elements;  Geological age strongly influences helium generation, with Paleoproterozoic (w(U)=8.9×10-6, w(Th)=22.4×10-6), Triassic (w(U)=7.8×10-6, w(Th)=18.7×10-6), and Carboniferous rocks exhibiting the highest helium generation intensity owing to prolonged decay and tectonic activities. The Triassic granites, in particular, show an average helium generation intensity of 0.94 nL/(g·Ma);  Sedimentary rocks demonstrate significant helium potential, with Early Cretaceous mudstone having a helium generation intensity (0.50 nL/(g·Ma)) equivalent to 53% of that of Triassic granite;  A strong positive correlation between w(U) and w(Th) (r=0.874) confirms the synergistic behavior of elemental geochemistry. This study establishes an evaluation system for helium source rocks and identifies Triassic granites, Paleoproterozoic granites and metamorphic rocks, and Cretaceous mudstones in the periphery of the Songliao basin as the highest-quality helium source rocks in Northeast China.

Key words: helium gas, helium source rock, uranium-thorium content, chronology, lithology-age coupling, helium strength, Songliao basin, Northeast China