Magmatic origin of geothermal fluids constrained by geochemical evidence: Implications for the heat source in the northeastern Tibetan Plateau

•High Cl, B, and Li concentrations are identified in the Geothermal fluids.•Geothermal fluids are found magmatic origin in northeastern Tibetan Plateau (NETP).•Parent geothermal fluid exists with temperature of 310 °C at depths of 6.8–7.8 km.•Partial melt zone exists and serves as additional heat source of Gonghe Basin.•Partial melt zone is ubiquitous in the middle to lower crust of the NETP.