滇西南澜沧断裂带温泉溶解无机碳释放通量与成因

Flux and Genesis of Dissolved Inorganic Carbon in Thermal Springs from the Lancang Fault Zone,Southwestern Yunnan

以青藏高原及其周边地区为代表的大陆碰撞带是现今全球最为典型的构造活跃区之一,但该地区活动断裂深部碳来源和释放通量的总体研究程度仍然不足。滇西南地区位于青藏高原东南缘,内部发育一系列左旋和右旋走滑断层,地震活动频发,水热活动丰富。对滇西南澜沧断裂带及其周边12个温泉的水化学组成和氢—氧同位素组成分析结果表明,温泉水为HCO_(3)-Na型,补给来源主要为大气降水,并受到围岩矿物溶解和离子交换反应的影响。基于溶解无机碳浓度与碳同位素组成的质量平衡模型揭示了深部碳对溶解无机碳的贡献比例为46.9%~78.0%,结合温泉水流量估算得到澜沧断裂带深部碳释放通量约为440 t/a,进而推算得到滇西南地区溶解无机碳深部碳释放通量约为3×10^(4) t/a。澜沧断裂带附近温泉的深部碳比例和释放通量均明显高于远离断裂带的温泉,证实走滑断层对深源含碳流体的形成和释放起到主要控制作用,为进一步理解滇西南地区活动断裂带深部碳释放的机制与规模提供了参考资料。

Degassing of CO_(2) from the solid Earth significantly influences the surface carbon cycle.In addition to volcanic activity,various types of active faults in nonvolcanic regions serve as crucial pathways for the migration and release of deep carbon to the surface.The continental collision zone,exemplified by the Tibetan Plateau and its surroundings,is one of the most tectonically active regions in the world.However,general research on deep carbon origins and outgassing rates of active faults remains limited.Southwestern Yunnan lies on the southeastern margin of the Tibetan Plateau and is characterized by a network of left-and right-lateral strike-slip faults.The area experiences frequent seismic events and abundant hydrothermal activity.The hydrochemical,hydrogen,and oxygen isotope compositions of 12 hot springs in the Lancang fault zone of southwestern Yunnan indicate that the hot spring water exhibits an HCO_(3)-Na type composition,primarily sourced from atmospheric precipitation,and shows no significant contamination from magmatic or metamorphic fluids.During subsurface fluid circulation,it undergoes mineral dissolution and ion exchange reactions with the surrounding rock minerals,which are influenced by the dissolution of minerals,such as silicates,carbonates,and evaporites.A mass balance model based on the concentrations of Dissolved Inorganic Carbon(DIC)and its carbon isotopic compositions shows that the contribution of deep carbon to DIC is approximately 46.9%~78.0%,which,together with the flow rates of thermal spring water,yield an estimated deep carbon outflux of approximately 440 t/a for the Lancang fault zone.The total deep carbon outflux of the thermal springs in southwestern Yunnan was estimated to be approximately 3×10^(4) t/a.The higher deep carbon fluxes and contributions observed in the thermal springs near the Lancang fault zone demonstrate the predominant influence of strike-slip faults on the origin and release of deeply sourced carbon-bearing fluids.Considering the tectonic context of the strike-slip movement,we suggest that the deformation and fracturing of deep rocks within the Lancang fault zone facilitated the migration of a significant volume of metamorphic CO_(2) and a minor portion of mantle-derived carbon to the shallow geothermal system.This process might have resulted in the formation of a reservoir enriched in CO_(2) fluids that could transfer carbon to the surface.These findings provide observational evidence that enhances our understanding of the mechanisms of deep carbon release in the active fault zones of southwestern Yunnan.