腾冲新生代火山区温泉CO2气体排放通量研究

近期研究表明,不仅火山喷发期会向当时的大气圈输送大量的温室气体,火山间歇期同样会释放大量的温室气体。在火山活动间歇期,火山区主要以喷气孔、温(热)泉以及土壤微渗漏等形式向大气圈释放温室气体。腾冲是我国重要的新生代火山区,同时也是重要的水热活动区,那里出露大量的温泉,然而目前未见腾冲火山区温泉气体排放通量的研究报道。本文利用数字皂膜通量仪测量了腾冲新生代火山区温泉中CO₂的排放通量。研究结果表明,腾冲新生代火山区温泉向当今大气圈输送的CO₂通量达3.58×10³ t·a^-1,相当于意大利锡耶纳Bassoleto地热区温泉中CO₂的排放规模。腾冲火山区温泉的CO₂释放通量主要受深部岩浆囊、断裂分布、地下水循环、围岩成分等多方面因素的影响。本文根据温泉中CO₂的排放特征,将腾冲温泉分为南北两区,南区温泉CO₂通量远高于北区的温泉,热海地热区的通量为腾冲CO₂通量的最大值。在北温泉区,CO₂通量主要受控于断裂的分布;而在南温泉区,除受到断裂控制外,热海地热区底部的岩浆囊及其与围岩的相互作用成为CO₂气体的重要物质来源,同时高温的岩浆囊为温泉及CO₂的形成提供了重要热源。

CO2 flux estimations of hot springs in the Tengchong Cenozoic volcanic field, Yunnan Province, SW China

Recent research results have indicated that, beside volcanic eruption periods, dormant periods in the intermittent between the volcanic activities can emit a large amount of the greenhouse gases into atmosphere. In the intermittent between volcanic eruptions, greenhouse gases are erupted from the volcanic eruptive fields in the forms of fumaroles, hot springs, soil micro-seepage and so on. Tengchong volcanic and geothermal system is one of the most important Cenozoic volcanic activity fields in China whereas the estimates of the greenhouse gases emitted from Tengchong have been poorly understood. Using a new apparatus named digital bubble flowmeter, we have measured the flux of bubbles in hot springs of the Cenozoic volcanic field in Tengchong. The estimated result shows that the flux of CO₂ from hot springs of Tengchong is up to 3.58×10³t·a^-1, which could be compared to the amount of the Bassoleto hydrothermal area in Siena, Italy. Based on the characteristics and distribution of the fluxes of CO₂ estimated, the hot springs in Tengchong can be divided into two areas: south area and north area. The emission of CO₂ in the south area is apparently higher than that in the north one and the largest one is located in Rehai area in the south area. The formation of CO₂ emitted from the hot springs is controlled by several factors, such as magma chamber temperature, fault penetrating, underground water circulation and country rock compositions.The flux of CO₂ is mainly controlled by fault activities in the north area whereas the flux of CO₂ in the south area is dominated by the magma chamber temperatures (e.g. Rehai). The magma chamber is thought to be one of the sources of CO₂, as well as it may contribute the hot springs with large amount of heat. However, fault activities may act as a pathway of the hot springs during their uprise .