The regional tectonic framework and some new understandings of the Middle-Lower Yangtze River Valley Metallogenic Belt

As one of the most important metallogenic belts in China, the Middle-Lower Yangtze River Valley Metallogenic Belt has experienced a long history of mining exploitation and regional geological research, and yielded fruitful achievements. In this paper, we discussed the tectonic framework, polygenetic compound tectonic system and timing of amalgamation between the Dongling/Picheng type basement and the Jiangnan type basement, proposed the concept of north-south confrontation zone, and defined the connotation of Jiangnan transition zone. The main understandings are as follows : (1) The planar tectonic framework of the Middle-Lower Yangtze River Valley Metallogenic Belt can be abstracted as " one arc and one line with two horns" ; (2) The amalgamation between the Dongling/Picheng type basement with the Jiangnan type basement occurred between Z(1) and Z(2); (3) The north-south confrontation zone is the key, which controlled the tectonic framework of the Middle-Lower Yangtze River Valley Metallogenic Belt; (4) The shearing is the eye, where diagenetic and metallogenic explosion of the Middle-Lower Yangtze River Valley Metallogenic Belt was took place during the transition from regional transpression to transtension; (5) The southern half of the Jiangnan transition zone was part of the Jiangnan uplift in the early stage, and it was folded together with the Lower Yangtze area during the Indosinian. The fold type of this area was similar to the southern margin of the Lower Yangtze depression, but different from the hinterland of the Jiangnan uplift. Therefore, it is classified as tectonic units in the Middle-Lower Yangtze River Valley Metallogenic Belt.