The Mid—Lower- Yangtze Tectonic Belt located in the interior of the Yangtze Craton is a peculiar lithospheric tectonic belt, and its origin has been a mystery. It was previously thought to be related to the subduction of the Late Jurassic Izanagi Ocean to Eurasia, but why did only the iron—copper and polymetallic ore belts form deeply inland in the Mid—Lower- Yangtze Tectonic Belt? To understand this problem, it is necessary to analyze the properties of the lithosphere and asthenosphere in the study area from geophysical data in South China, and make global comparisons of similar structures. Based on the results of geophysical surveys, the crust of the tectonic belt in the Mid—Lower- Yangtze Tectonic Belt mainly reflects the characteristics of grabens. The lithosphere exhibits low S- wave velocities and high densities. Such shallow mantle dynamic tectonic system was close to the pattern of subduction of mid- ocean ridges to continents. Based on the Jurassic—Cretaceous oceanic magnetic anomaly bands and paleomagnetic studies in the Pacific region, it can be speculated that the formation of the Mid—Lower Yangtze Tectonic Belt and the iron—copper polymetallic ore belt could be the results of subduction of the northern Izanagi ocean ridge and related triple ridge junction to the Yangtze Craton. Of course, more survey data is needed to prove this conjecture.