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Magmatic origin of geothermal fluids constrained by geochemical evidence: Implications for the heat source in the northeastern Tibetan Plateau
Journal of Hydrology ( IF 6.4 ) Pub Date : 2021-09-24 , DOI: 10.1016/j.jhydrol.2021.126985
Sheng Pan 1, 2, 3 , Yanlong Kong 1, 2, 3 , Ke Wang 1, 2, 3 , Yaqian Ren 1, 2, 3 , Zhonghe Pang 1, 2, 3 , Chao Zhang 4 , Dongguang Wen 5 , Linyou Zhang 5 , Qingda Feng 5 , Guilin Zhu 5 , Jiyang Wang 1, 2, 3
Affiliation  

The northeastern Tibetan Plateau (NETP) represents the growth front of the Tibetan Plateau (TP) system. This region has long been recognized as a key in understanding the topographic response and crustal thickening of the entire TP. A heat flow anomaly (Gonghe Basin, 102 mW/m2) was found in the NETP. However, the heat-generation mechanism and the heat source of the Gonghe Basin are still debated as it is unclear whether they are related to magmatic melting activities. Herein, we provide systematic hydrogeochemical data of two types of geothermal waters (type I and II: geothermal waters sampled from within the basin and the mountainous regions, respectively) found in the region. Type I high δD (−85.0‰ to −59.0‰), δ18O (−11.1‰ to −8.0‰), Cl (mostly range from 300 to 900 mg/L), and trace element, whereas type II has low δD (−97.1‰ to −89‰), δ18O (−13.0‰ to −11.8‰), Cl (30 to 180 mg/L) and trace elements. Furthermore, we identified the existence of a high-temperature parent geothermal fluid based on the chloride – enthalpy model, it was estimated to possess a temperature of 310 °C and a circulation depth of 6.8–7.8 km. The parent geothermal fluid originated from snowmelt water, which later mixed with a magmatic fluid. The helium (He) ratios of geothermal gas ranged from 0.01 Ra to 0.18 Ra and indicated that the source of He was primarily from a crustal source. In addition to the heat flow analysis and magnetotelluric (MT) data, we suggested that the magmatic nature of the geothermal fluid is caused by a partial melt zone, which is ubiquitous in the middle to lower crust and serves as the heat source in the NETP. Finally, a conceptual model was built to illustrate the occurrence of magmatic fluid and its genesis. The findings will help to improve the understanding of the uplift of the TP and reveals the important role of deep groundwater circulation in the formation of high-temperature geothermal resources.



中文翻译:

受地球化学证据约束的地热流体岩浆成因:对青藏高原东北部热源的启示

青藏高原东北部(NETP)代表青藏高原(TP)系统的增长前沿。该区域长期以来被认为是理解整个青藏高原地形响应和地壳增厚的关键。在 NETP 中发现了一个热流异常(共和盆地,102 mW/m 2)。然而,共和盆地的发热机制和热源是否与岩浆熔融活动有关尚不清楚。在此,我们提供了该地区发现的两种类型地热水(类型 I 和 II:分别从盆地和山区采样的地热水)的系统水文地球化学数据。I型高δD(-85.0‰至-59.0‰),δ 18 O(-11.1‰至-8.0‰),Cl -(主要范围为300至900 mg / L)和微量元素,而II型具有低δD(-97.1‰至-89‰),δ 18 O(-13.0‰至-11.8‰),Cl -(30 至 180 毫克/升)和微量元素。此外,我们根据氯-焓模型确定了高温母地热流体的存在,估计其温度为310°C,循环深度为6.8-7.8 km。母地热流体起源于融雪水,后来与岩浆流体混合。地热气的氦(He)比范围为 0.01 Ra 至 0.18 Ra,表明 He 的来源主要来自地壳源。除了热流分析和大地电磁 (MT) 数据外,我们认为地热流体的岩浆性质是由部分熔融带引起的,该带在中下地壳普遍存在,并作为 NETP 的热源. 最后,建立了一个概念模型来说明岩浆流体的赋存及其成因。

更新日期:2021-09-30
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