Major Characteristics of the Lajishan Orogenic Belt of the South Qilian Mountains and Its Geotectonic Attribute

The Lajishan orogenic belt is one of the E-W-trending Caledonian erogenic belts within the Qinling-Qilian orogenic system. It was formed upon the Jiningian basement by intensive taphrogenesis. Its major characteristics comprise the prominent faulting along the north and south boundaries, the highly complicated petrological and petro-geochemical features of the volcanic rock series, and the development of a new type of ophiolite suite. In terms of tectonic analysis and the sequential analysis of tectonic settings of magmatic rocks, it is suggested that the Lajishan orogenic belt has undergone a complete "opening-closing" cycle, which can be further divided into 3 second-order "opening-closing" cycles. The composite characteristics of the "opening-closing" movement show that Laji Mountain is a typical fault orogenic belt. The fault orogenic belt is one of the most important types of intracontinental orogens. It is of critical theoretical and practical significance to summarize the characteristics and the diagnostic criteria of this kind of orogenic belts, and study the mechanism of their formation and build models of their evolution.