Relationship between radiogenic heat production in granitic rocks and emplacement age

Granites play a crucial role in the Earth's thermal regime and its evolution.Radiogenic heat production(RHP)by the decay of radioactive elements(U,Th,K)in granites is a significant parameter in estimating the thermal structure of the lithosphere.RHP variability of granites with their emplacement ages could provide insights for thermal modeling in different geological epochs.An aggregated RHP from 2877 globally-distributed granitic samples of continental crust are analyzed for this study;these sample cover the entire geological history.The average bulk RHP in all types of granitic rocks of all ages is 2.92±1.86μW/m^(3).The RHP tends to increase gradually with progressively younger geologic emplacement age,based on a statistical analysis of the data.However,the youngest granites do not necessarily have the highest RHP.The mean RHP in 181 representative Cenozoic Himalayan leucogranitesdwhich are the youngest granites found on Earth,is as low as 1.84μW/m^(3).This is probably related to the initial conditions of magma formation,magmatic source material,and differentiation processes in the HimalayaneTibetan plateau.By correcting the decay factor,variations of the RHP in the emplaced granitic rocks are obtained,indicating the changing levels of heat production and different thermal regimes on Earth in various geological epochs.The highest RHP in granitic rocks emplaced in the Archean and Early Proterozoic corresponds to two global-scale collisional events during supercontinent cycles,at 2.7 and 1.9 Ga respectively.RHPs of granites can be an important indicator in the study of Earth's thermal regime and its evolution.

Heat Aggregation Mechanisms of Hot Dry Rocks Resources in the Gonghe Basin, Northeastern Tibetan Plateau

Hot dry rock(HDR) is an important geothermal resource and clean energy source that may play an increasingly important role in future energy management. High-temperature HDR resources were recently detected in deep regions of the Gonghe Basin on the northeastern edge of the Tibetan Plateau, which led to a significant breakthrough in HDR resource exploration in China. This research analyzes the deep temperature distribution, radiogenic heat production, heat flow, and crustal thermal structure in the Qiaboqia Valley, Guide Plain, and Zhacanggou area of the Gonghe Basin based on geothermal exploration borehole logging data, rock thermophysical properties, and regional geophysical exploration data. The results are applied to discuss the heat accumulation mechanism of the HDR resources in the Gonghe Basin. The findings suggest that a low-velocity layer in the thickened crust of the Tibetan Plateau provides the most important source of constant intracrustal heat for the formation of HDR resources in the Gonghe Basin, whereas crustal thickening redistributes the concentrated layer of radioactive elements, which compensates for the relatively low heat production of the basal granite and serves as an important supplement to the heat of the HDR resources. The negative effect is that the downward curvature of the lithospheric upper mantle caused by crustal thickening leads to a small mantle heat flow component. As a result, the heat flows in the Qiaboqia Valley and Guide Plain of the Gonghe Basin are 106.2 and 77.6 m W/m2, respectively, in which the crust-mantle heat flow ratio of the former is 3.12:1, indicating a notably anomalous intracrustal thermal structure. In contrast, the crust-mantle heat flow ratio in the Guide Plain is 1.84:1, which reflects a typical hot crust-cold mantle thermal structure. The Guide Plain and Zhacanggou area show the same increasing temperature trend with depth, which reflects that their geothermal backgrounds and deep high-temperature environments are similar. These results provide important insight on the heat source mechanism of HDR resource formation in the Tibetan Plateau and useful guidance for future HDR resource exploration projects and target sites selection in similar areas.