腾冲火山区温室气体释放规模及其深部碳循环意义

Concentrations of the greenhouse gases in the atmosphere result from the natural emissions and human activities. Determining the proportions of the two types of greenhouse gases is a critical issue and prerequisite for the further negotiations focusing on the climate changes among countries. Cenozoic volcanic active field is thought to be one of the important sources of geological greenhouse gases. The sum of flux of the greenhouse gas emissions from these Cenozoic volcanic fields is still unclear in spite of the spatial distributions of numerous Cenozoic volcanoes in China. Tengchong Cenozoic volcanic field is located on the southeast margin of the Tibetan Plateau, which is a consequence of the Indian-Asian collision and subsequently northward subduction of the India. Intense hydrothermal activities (including hot springs and soil micro-seepage) occur in this volcanic field, which is thus thought as a potential important degassing area of the intra-continent subduction-induced volcanic activities-sourcing greenhouse gases in China. We will estimate the flux of the greenhouse gases released from the Tengchong volcanic field and further explore the mechanism of deep carbon cycle in the continental collision-related geodynamic setting in order to provide the scientific-based data of the greenhouse gases erupted from the Tengchong volcanic field in the future negotiations focusing on the global climate changes among countries. Our results would be of significant help for the climate-change negotiations and developing a robust model to explain the processes of deep carbon cycles in continental collision zones.

温室气体排放与国家发展息息相关。当前大气圈中温室气体浓度是自然因素和人类活动共同作用的结果。从科学上厘清自然和人类活动在导致温室气体浓度变化中的比例是气候变化谈判中划分减排份额和进行谈判的重要基础与前提。火山是重要的地质源温室气体来源之一。我国境内有多座新生代休眠火山。然而，由于尚未进行全面研究，我国大陆新生代火山区每年向大气圈释放温室气体的总量至今仍是未知数，严重制约了我国在气候谈判中的主动权。腾冲火山区位于青藏高原东南边缘，受印度-欧亚大陆碰撞及印度大陆俯冲影响，火山区内具有多种类、强烈的水热活动形式，是研究青藏高原周缘火山区温室气体释放通量特征的理想场所。本项目拟综合岩石学与气体地球化学等多种研究方法，在前期研究基础上对腾冲火山区温室气体释放通量进行研究。通过系统野外测量，获得国际上认可的腾冲火山区温室气体释放通量高精度数据，为我国在日趋严峻的国际气候谈判中争取国家利益提供科学依据。

本项目通过详细野外调查和取样，对腾冲火山区温室气体释放通量和成因进行了系统性研究；该项目所提出的各项研究计划，均已经顺利执行并圆满完成。研究结果表明，腾冲火山区土壤CO2平均释放通量介于25~875 g m-2 day-1之间，区内每年通过温泉逸出气、温泉溶解气、土壤微渗漏等方式向大气圈释放的CO2约为4.5-7.1 Mt，无论是CO2释放通量还是总量均明显高于我国东北典型新生代火山区。腾冲火山区内存在明显的岩浆脱气现象，其深源气体释放与地下岩浆房的空间分布密切相关。研究区温泉气体的He-C同位素耦合模型研究结果显示，腾冲火山区释放的温室气体与印度大陆俯冲存在成因联系。本项目探讨了印度-亚洲大陆汇聚背景下俯冲沉积物、富集地幔楔与陆壳碳酸盐岩相互作用的碳释放机制，提出印度大陆俯冲组分造成地幔楔富集过程，导致了富CO2熔（流）体脱气，其产生的挥发分同时受到陆壳碳酸盐岩混染。本研究所获得的上述认识为深入理解大陆碰撞带挥发分再循环机制提供了新的证据与研究资料。