腾冲火山区的现代幔源氦释放:构造和岩浆活动意义  

Present-day mantle-derived helium release in the Tengchong volcanic field,Southwest China:Implications for tectonics and magmatism

作　　者：赵慈平[1] 冉华[1] 王云[1] 

机构地区：[1]云南省地震局,昆明650224

出　　处：《岩石学报》2012年第4期1189-1204,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金(40973015;41172306)资助

摘　　要：深地震测深(DSS)和大地电磁测深(MT)都表明腾冲火山区现今仍存在壳内岩浆囊,但对其数量和空间分布还存在分歧并缺乏全貌性认识。MT探测认为腾冲火山区是一个软流圈上涌和岩石圈减薄区,但对这一减薄区的空间范围还缺乏充分的约束。通过对腾冲火山区及外围大范围温泉逸出气体的分析测试,我们共获得了75个温泉逸出气体的氦同位素3He/4He比值数据(部分为前人资料)。利用氦同位素示踪原理,我们研究了腾冲火山区幔源氦释放强度空间分布和时间变化特征,结果发现:腾冲火山区的幔源挥发份释放呈1带3区分布。以3He/4He≥1Ra,幔源氦比例≥15%为界,腾冲火山区的幔源挥发份释放异常区呈整片分布,为一南北走向的条带,南北长100km,东西宽50km。在整片异常区的内部,腾冲火山区的幔源挥发份释放又有强度不同的3个区域:①中部腾冲县城-热海一带,3He/4He比值达到5.5Ra以上,幔源氦比例达到70%以上,释放强度最强。②北部曲石一带,3He/4He比值达4.5Ra以上,幔源氦比例达到50%以上,释放强度次之。③南部五合-蒲川-新华一带,3He/4He比值达2Ra以上,幔源氦比例达到25%以上,释放强度最弱;腾冲火山区幔源挥发份释放强度在不断升高,其中第3个释放区的3He/4He比值(Ra)升高速率比前两者明显要大。我们认为:腾冲火山区现今幔源挥发份释放强度的空间分布图象就是该地区软流圈上涌和岩石圈减薄区空间尺度和上涌强度的最直接反映,上涌区(减薄区)的大小大致为南北长100km,东西宽50km;腾冲火山区现今存在3个壳内岩浆囊。第1个岩浆囊位于腾冲县城-热海一带,第2个岩浆囊位于马站-曲石一带,第3个岩浆囊位于五合-龙江-团田-蒲川-新华一带;腾冲火山区3个岩浆囊都在不断受到幔源岩浆的持续补充;第1个岩浆囊集幔源挥发份释放、相对地热梯度、地壳形变和地震活动等异常于一身,活Both deep seismic sounding（DSS） and magnetotelluric sounding（MT） data suggest that there exist still magma chambers within crust in Tengchong volcanic field（TVF） present-day,but there are differences on their number and spatial distribution and their complete picture still lack good understanding,MT data suggests that TVF is an asthenosphere-upwelling and lithosphere-thinning area,but the spatial extent of the thinning area still lack adequate constraints,By sampling,istopic analyzing of free gases from thermal springs in TVF and its periphery area,and utilizing some previous investigation data,we obtain 3He/4He ratio data of 75 thermal springs,By atmosphere contamination correcting,mantle-derived proportion calculating and spatial interpolation,we obtain spatial distribution map and time diagram of release intensity of mantle-derived volatiles in TVF,After investigating the characterization of spatial and temporal distribution of mantle-derived helium release according helium isotope tracing principle,we found that there are 1 band and 3 blocks of high 3He/4He ratio in spatial distribution pattern in TVF,With 3He/4He≥1Ra（Ra denotes the atmospheric 3He/4He ratio value,1.39×10-6）,mantle-derived helium proportion≥15% as boundary conditions,the abnormal release area of mantle-derived volatiles in TVF shows an entire zonal area,which is a north-south strike strip,north to south 100km long,east to west 50km wide,In the whole piece of abnormal area inside,the intensity of mantle-derived volatile release can be divided into 3 different areas,① The Tengchong County-Rehai and periphery in central TVF,where the 3He/4He ratio reaches more than 5.5Ra,the mantle-derived helium proportion above 70%,are the most strong release area,② The Qushi and periphery in north TVF,where the 3He/4He more than 4.5Ra,the mantle-derived helium proportion more than 50%,are second strong release area;③ The Wuhe-Puchuan-Xinhua in southern TVF,where the 3He/4He more than 2Ra,the mantle-derived helium proportion more tha

关 键 词：腾冲火山区 氦同位素 软流圈上涌 岩石圈减薄 岩浆活动 温泉逸出气体 

分 类 号：P315.3[天文地球—地震学]