Geothermal Accumulation Constrained by the Tectonic Transformation in the Gonghe Basin, Northeastern Tibetan Plateau

Abstract

Abstract Advances in the exploration of the geothermal resources with remarkably high temperatures in the Gonghe Basin, northeastern Tibetan Plateau, provide an enhanced understanding of the origin and emplacement of hot dry rock (HDR). Based on the integrating analysis on the boundary faults distribution and their activity histories, springs and geothermal borehole data, and magnetotelluric data, we propose that the Gonghe Basin formed in a zone of slip dissipation between two major large-scale left-lateral strike-slip faults of the Kunlun fault to the south and the Haiyuan fault to the north during the Neogene time. During the evolution of these two major strike-slip faults, the basin has experienced two-phase developments: the transrotational Gonghe-Qinghai lacustrine basin system during the Miocene and the transpressional Gonghe-Tongde basin system during the Pliocene-Quaternary. In response to the crustal transtension components of the transrotational Gonghe Basin, the partial melting zone at depths of 10–25 km in the thickened crust (~54 km) has been uplifted by ~10 km compared with adjacent regions since the Pliocene. This uplifted partial melting zone may have provided prominent potential heat energy for the HDR in the Triassic granitoid batholith at shallower depths (~3–10 km) by effective enhancement of the geothermal conduction process via deep faulting. With obliquely south-verging thrusting of the Gonghe Nan Shan thrusts in the northern, the Gonghe Basin has transformed from transrotation to transpression-domination during the 6–3 Ma, as well as accompanying with the depocentre migrating to the northwest and in turn the basement elastically uplifting in the southeast. This differential deformation of the basin floor has resulted in a northeastward upward tilting of the Triassic batholith and an isothermal surface. It finally developed the high-temperature and shallow-burial HDR with anomalously temperatures of over 100°C at a depth of 1.5 km in the Qiabuqia and Zhacang geothermal areas in the Gonghe Basin, NE margin of the Tibetan Plateau.