Cretaceous Volatile Fluxes from Intermediate-Acid Volcanism in NE China: Climatic Perturbations Triggered by Songliao...

Quantifying the amount of sulfur (S) released by magmatic activity is very important to accurately assess the climate impact caused by volcanic activity, but it is challenging for pre-Quaternary magmatic activity. During the Aptian-Albian period, the Songliao Basin experienced intense volcanic activity, resulting in the formation of a large volume of volcanic rocks. Among them, the intermediate-acid volcanic rocks of the first member of the Yingcheng Formation were formed in the middle to late Aptian and are characterized by wide distribution and considerable thickness. In addition, the southeastern margin of the Songliao Basin offers excellent outcrop conditions. By detecting the compositions and contents of major and volatile elements in the primary melt inclusions, the melt inclusions are divided into three types according to the evolution stages by the CaO/Al₂O₃ ratio: Type I (primitive), Type II (relatively evolved) and Type III (most evolved), and Type III melt inclusions are used to replace the missing matrix glass in the parent rock. The aerosols formed by the sulfur release that estimated by the "petrological method" led to the temperature drop in the region, which is consistent with the KAp4 sea level decline event. The study area (5.02 km²) is only 0.019% of the area of the Songliao Basin (2.6 × 10⁴ km²), so the degassing amount of intermediate-acid magma in the first member of the Yingcheng Formation in the whole Songliao Basin was enormous. It is not common to replace matrix glass with melt inclusions that formed in late magmatic evolution, but this may provide a new idea for studying the degassing of pre-Quaternary magmatic activities.