摘要
利用地球物理资料分析了腾冲火山区的深部构造特征,针对岩浆囊的数量、规模、传输通道以及地幔源区等问题进行了讨论.分析表明,腾冲火山区存在三个尚未完全固结的岩浆活动区域,它们分别位于黑空山、热海以及五合-团田一带.其中黑空山和热海附近的岩浆囊深度在5~25km之间,水平方向达到15~20km,而五合-团田一带岩浆囊的构造特征尚不能确定.上述岩浆囊通过浅部通道与黑空山、小空山以及热海相连,目前还不能判明打鹰山、马鞍山、老龟坡、来凤山等最新一期的火山下方是否存在类似的岩浆囊,也不清楚它们通过怎样的传输通道与已知的壳内岩浆囊相连.一些重要断裂如腾冲断裂、大盈江断裂和龙陵断裂,特别是这些断裂的交汇部位有可能成为连接壳内岩浆囊和上地幔源区的通道.与周边地区相比,腾冲火山区的岩石圈厚度明显减薄,高热活动与印缅块体向东俯冲有密切的联系:岩石圈板片下沉导致地幔上涌和弧后扩张,热流物质穿过壳幔边界进入地壳形成岩浆囊,也不排除中生代以来Sagaing断裂右旋剪切产生的深部效应.尽管腾冲火山区深部动力过程的构造轮廓日渐清晰,仍需开展高分辨地球物理探测才能揭示壳内岩浆系统和传输通道的细节,以便合理建立火山区岩浆活动的构造模型.
We analyzed deep structures of the Tengchong volcanic area from existing geophysical data,and focused on the numbers and scales of magma chambers,heat flow channels and mantle sources.The analysis reveals three areas probably underlain by unconsolidated magma sources.They are located in the Heikongshan volcano,Rehai geothermal field and WuheTuantian area respectively.Among them,the magma sources in the Heikongshan and Rehai have a depth range of 5~25km,with lateral scale of 15~25km,whereas the geometry of the magma source in the Wuhe-Tuantian is not well determined.Those magma sources are connected the Heikongshan,Xiaokongshan volcanoes and Rehai geothermal field through shallow channels.However,it is not clear if those younger volcanoes like the Dayinggshan, Maanshan, Laoguipo,Laifengshan are underlain by similar unconsolidated magma sources.We are not sure that in which way they connect the better known magma sources?Some significant faults,such as Tongchong fault, Dayingjiang fault and Longling fault,particularly the conjunctive areas between them are believed to be pathways to link crustal magma chambers with mantle sources.Compared to surrounding regions,the Tengchong volcanic area is underlain by a thinned lithosphere.High heat flows is related to the eastward subduction of the India-Burma plate:sinking of the lithospheric slab resulted in the mantle upwelling and back-arc extension,which made hot materials going up through crust-mantle boundary and forming the magma chambers within the crust.It doesn't exclude the roles of the dextral shearing of the Sagaing fault on deep structures since Mesozoic. Although the dynamic process and deep tectonic frame of the Tengchong volcanic area are more and more clear, it still requires high-resolution geophysical investigations to provide detail information of the magma chambers and transportation pathways within the crust,so as to establish appropriate tectonic models for magma activities of the Tengchong volcanic area.