西藏东南缘地热泉华的地球化学特征和成因

Geochemical Characteristics and Origin of Sinters in the Southeastern Margin of Tibet

青藏高原水热活动强烈,热泉分布广泛,泉华常伴随水热活动沉积,其中富含大量矿产资源。泉华的矿物组成和微量元素特征可用来示踪地热矿源和循环演化的路径。西藏东南缘地热资源与中部差异较大,八宿和德达泉华的微量元素含量整体低于藏中(前者为上地壳的n×10^-5~n×10倍,后者在n×10^-3~n×10^3倍),其Li、Rb、Cs等元素含量更是低于藏中(前者低于后者数十倍甚至百倍)。出现这种差异的原因主要是地热水水源、冷热水混合比例、径流时间和循环深度的不同及基底的差异;八宿和德达泉华的稀土元素配分曲线为左倾型,藏中为右倾型,系地热水类型不同所致。八宿和德达地区的地表水沿深大断裂下渗受地温梯度和深部部分熔融层的循环加热,温度升高形成地热水,最终出露地表沉积形成泉华。

The Tibetan plateau,a lab of global hydrothermal activity learning,has strong geothermal activities and all kinds of geothermal spring.The mineral composition and trace elements contents of sinters,normally deposited by hydrothermal activities,can reflect the origin or the cyclic model of geothermal activities.The contents of trace elements in sinters from eastern Tibet are dozens of times higher than those from the central Tibet,particularly in Li,Rb and Cs.Besides,the REE distribution curves at Basu and Deda regions are left-inclined types in contrast to those at the central Tibet.By the combination of all geochemical characteristics,we come to the conclusion that differences of water sources,mixing ratio of geothermal water and cold water,circulation depth and terrain’s basements are the main causes of different geochemical characteristics of sinters from eastern Tibet and central Tibet.