Natural Radioactivity Logs and Interpretation from the CCSD Main Hole

In order to understand the vertical distribution of natural radioactivity of the upper crust of the ultra-high pressure (UHP) metamorphic belt in Donghai County, Jiangsu province, as well as the influence of the retrogression intensity of eclogite on the concentration of radioelement, and the influence of radiogenic heat production rate on the geothermal gradient, the natural radioactivity logs (gamma ray and gamma spectrometry logs) from the main hole of the Chinese Continental Scientific Drilling (CCSD) were utilized to obtain the natural gamma intensity and the concentration of U, Th and K of main lithologies and the heat production rate log. The natural gamma intensity and concentration of U, Th and K gradually increase from serpentine to eclogite, amphibolite, paragneiss, and orthogneiss. With the strengthening of the retrogression of eclogite, the concentration of U, Th and K of eclogite increase. This indicates that some exotic fluids with U, Th and K elements join in the retrograde metamorphism. The vertical distribution of the natural gamma intensity and concentration of U, Th and K is dominated mainly by lithology. The natural gamma intensity approximately increases with the depth. The heat production rate and the natural gamma log have a good linear relationship. The formation with high radioactivity could cause disturbance and low anomalies on geothermal gradient on its upper formation.