Thermal evolution of the Upper Yangtze Craton: Secular cooling and short-lived thermal perturbations

Abstract

The Upper Yangtze Craton (UYC) has stayed in a long-term stabilization state. Its thermal history can be portioned into two parts: secular evolutionary trend and short-lived thermal perturbations. The former is simulated by a two-dimensional forward transient thermal model, and the latter is discussed by reviewing previous studies. The numerical modeling indicates the UYC tended to be cooling as it adjusted to the asynchronous rates of change in the internal radiogenic heat production and in the convecting mantle temperature below the cratonic root. The average cooling rate of the UYC has been ~58 °C/Ga since the end of Archean, faster than that of the convecting mantle. The surface heat flow presents a decreasing trend from ~82 mW/m2 at 2.5 Ga to ~53 mW/m2 at present-day, which constructs the long-term evolutionary path. The thermal perturbations derived from the occasional tectono-thermal events, such as mantle plume activity and regional lithosphere extension, serves as paroxysmal factors. The thermal effects of the Emeishan mantle plume were very strong, yielding to the maximum heat flow anomaly of ~100 mW/m2 at the Late Permian. In contrast, the influences of regional lithosphere extension during both the early Paleozoic period and the Early Permian-Middle Triassic period were rather weak, resulting in a surface heat flow increase of <10 mW/m2. These thermal anomalies disappeared after a time period depending on the thermal relaxation without altering the stability of the UYC, and then the thermal evolution of craton returned to its original cooling route. The thermal history of the UYC, the overprinting of the secular cooling and the short-lived perturbations, helps better understand the craton evolution and provide the fundamental thermal data for petroliferous-basin analysis.