青海共和盆地岩石圈热-流变结构及地热意义

Lithospheric Thermal-rheological Structure and Geothermal Significance in Gonghe Basin,Qinghai Province

地球深度热状况是深部地球动力学和岩石圈活动性研究的重要内容,岩石圈热结构和热-流变结构可以很好地揭示岩石圈范围内的热状况。近年来,在青海共和盆地钻探揭露了深部高温干热岩体,关于其热源机制尚未有定论。本文以青海共和盆地为研究对象,分析壳内温度分布和流变强度,探讨壳内低速体的地质属性。结果表明,共和盆地的地壳流变结构从上而下分为脆性和韧性两层,韧性层又包括中地壳和下地壳两层韧性层,在上地壳尺度均表现为脆性破裂为主,并逐渐过渡为韧性流变;恰卜恰地区在脆性破裂的上地壳延伸至中下地壳时,破裂沿一系列滑脱面发生韧性滑动,局部地段形成壳内熔融,为恰卜恰地区提供了额外的热源,使其大地热流值(109.6 mW/m^(2))显著高于贵德地区(77.6 mW/m^(2))。这一认识为共和盆地壳内低速体存在提供了新的佐证,也为区内干热岩热源分析以及高温地热资源探测开发提供了科学依据。

The thermal condition of the Earth at depth is an important element in the study of deep geodynamics and lithospheric activity,and the lithospheric thermal structure and thermal-rheological structure can well reveal the thermal condition in the lithospheric range.In recent years,drilling activities in Qinghai Gonghe Basin have revealed deep high-temperature hot dry rocks,about which the heat source mechanism has not been conclusively established.In this paper,we take Gonghe Basin in Qinghai as the research object,analyze the intracrustal temperature distribution and rheological intensity,and explore the geological properties of the intracrustal low-velocity body.The results show that the crustal rheological structure of Gonghe Basin is divided into brittle and ductile layers from top to bottom,and the ductile layer includes two ductile layers,the middle crust and the lower crust,all of which show mainly brittle rupture at the upper crustal scale and gradually transition to ductile rheology.In the Qiaboqia region,when the brittle rupture of the upper crust extended to the middle and lower crust,the rupture occurred along a series of slip surfaces with ductile sliding,and intracrustal melting was formed in local sections,which provided additional heat source for the Qiaboqia region and made its geothermal heat flow value(109.6 mW/m^(2))significantly higher than that of the Guiade region(77.6 mW/m^(2)).This understanding provides new evidence for the existence of low-velocity bodies in the crust of Gonghe Basin,and also provides a scientific basis for the analysis of heat sources of hot dry rocks in the region and the exploration and development of high-temperature geothermal resources.