Enrichment background and formation mechanism of middle- and deep-geothermal resources in the Fenwei Graben

doi:10.13745/j.esf.sf.2024.1.10

Abstract

Abstract:

Geothermal resources in the middle and deep layers of the Fenwei Graben exhibit considerable development, yet their genetic mechanism remains elusive. A thorough understanding of the geological background and the cause of thermal convergence is essential for improving exploration and exploitation efficiency. Building on previous research, this paper provides a comprehensive analysis of the deep thermal structural characteristics, structural evolution, genetic mechanisms, and the source, migration pathways, reservoirs, and sealing conditions of the Fenwei Graben. Additionally, it explores the mechanisms of driving thermal convergence in the region. The formation of middle and deep geothermal resources in the Fenwei Graben is rooted in a complex geological framework, with Cenozoic tectonic processes playing a pivotal role in the development of medium- and high-temperature reservoirs. The Cenozoic extension of the Fenwei Graben is primarily driven by the distant effects of the Indian-Eurasian plate collision. Key factors contributing to the formation of geothermal resources in the region include asthenospheric diapir upwelling, the development of low-velocity, high-conductivity zones in the middle and shallow layers, crustal stretching and thinning, and solid-shear ductile deformation. Mantle heat conduction serves as the primary dynamic heat source for the target geothermal reservoir, with shallowly embedded low-velocity, high-conductivity layers within the upper mantle and crust acting as efficient heat conductors and energy accumulation centers. These layers function as direct heat sources and focal points for medium- and deep-thermal reservoirs. The significant extension and tension during the Cenozoic era, combined with distinct structural patterns, provide favorable thermal control structures. Marginal faults and basin-controlling faults, characterized by deep incisions and active Cenozoic tectonics, exhibit excellent heat conduction properties, playing a crucial role in the formation and distribution of geothermal resources. These faults act as efficient pathways for heat conduction and release. The thick Cenozoic loose sediments with extensively developed pores, along with volcanic rocks characterized by low thermal conductivity and excellent heat retention, serve as high-quality thermal capping layers. The metamorphic basement, marked by ductile shear deformation, functions both as the target layer for dry hot rock geothermal resources (solid heat energy) and as an effective heat source layer for shallow hydrothermal geothermal systems. As a result, the Fenwei Graben boasts an exceptional thermal accumulation system, integrating heat sources, pathways, reservoirs, and capping layers, which collectively support the enrichment of high-quality geothermal resources.

Key words: geothermal resources, geothermal system, thermal control structure system, formation mechanism, Fenwei Graben

CLC Number:

P314
P541

LIU Demin, ZHANG Changsheng, LU Wanling, WEI Meihua, QI Yanya, LIU Fei, ZHAO Yue, JIANG Huai. Enrichment background and formation mechanism of middle- and deep-geothermal resources in the Fenwei Graben[J]. Earth Science Frontiers, 2025, 32(1): 367-379.

Figures/Tables 6

Fig.1 Sketch map of regional tectonics in the Fenwei Graben. Modified after [4-5].

Fig.2 Sketch map of subdivision secondary structural units in the Fenwei Graben

Fig.3 Geological structure profile of Fenwei Graben. Modified after [16].

Fig.4 Depth map of Curie and Moho surfaces in the Fenwei Graben. Modified after [16,21,23].

Fig.5 Distribution map of source depth of strong earthquakes and Curie isothermal surface in the Fenwei Graben. Modified after [17].

Fig.6 Schematic diagram of extensional faulted basins and the genetic mechanism of thermal reservoirs in the Fenwei Graben

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