New structural observations of Oligo‐Miocene deformation in north Vietnam along the Red River Shear Zone suggest that left‐lateral strike‐slip shear was restricted to the upper and middle crust above a horizontal shear zone. Left‐lateral shear deformation is associated with low‐pressure‐low‐temperature parageneses. High‐temperature deformation is restricted to zones where the foliation has a low dip in the core of the Dai Nui Con Voi antiformal dome. These observations complete those made earlier in the Bu Khang extensional dome farther south. Above the horizontal shear zone left‐lateral transpression was active during the first stage and changed to transtension some 33 Myr ago. Purely extensional metamorphic domes (Bu Khang) or transtensional domes (Dai Nui Con Voi) were exhumed during this younger stage. Our observations plead for caution when interpreting strike‐slip structures at lithospheric scale.
Geologic characteristic controls the development of high-flux hydrothermal conduits that geothermal system formation which is evaluated at large and small scales in the Northern part of Vietnam. There are also several active fault zones here including the Red River fault zone (RRFZ), and Dien Bien-Lai Chau fault zone (DBLCFZ) which have been shown by the previous study. However, the investigation for geothermal potential relating to these fault zones has not been implemented yet. Therefore, this work has made a synthesis of geothermal potential in Northern part of Vietnam basing on the geostructural, geochemical and geophysical data. It shows the first study for the assessing of the geothermal potential of DBLCFZ which is based on the presence of hot springs at the southern DBPB (Uva geothermal reservoir). This study focuses on the deformation characteristics of fault, determining the heat source basing on both electrical field geophysical data and geo-thermometric calculations of K+-Na+cations from thermal water in this area, in combination with the assessment of groundwater potential by the hydrogeological survey. The result shows that firstly the hot spring phenomenon at Uva geothermal reservoir (with flow rate attending to 216m3 per day) which is related to the DBLCFZ, and secondly, the geothermal potential in Uva area belongs to medium level in the worldwide classification grade with the calculated heat source is up to 145,3oC in average. Considerations on the restorable capacity of groundwater and its geothermal potential, this result suggests that the geothermal source of Uva can be used to build a geothermal power plant on a small scale.
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