DIVISION AND CHARACTERISTICS OF THE GEOTECTONIC UNITS OF YUNLING EPICONTINENTAL ARC IN NORTHWEST YUNNAN

With field survey and data processing, the structural characteristics of the Yunling epicontinental arc in Northwest Yunnan are clarified. This region is divided into 6 four-grade tectonic units, i.e. Xuelongshan Rock Group (Pt₁Xl), Deqing Blocks (Pz₁), Pantiange acidic volcanic magmatic arc (T₂), Gongnong inter-arc basin (T₂), Cuiyibi intermediate-basic volcanic magmatic arc(T_1-2), and Ludian volcanic arc-syn-collisional granite(T). The former two units belong to the basements of island arcs; while latter four, the main bodies. The rock associations and deformation-metamorphism of each unit are various obviously. The main bodies of island arcs were formed from Early Triassic to early Late Triassic, as a product of the westward subduction and collisional orogeny of Jinshajiang ocean basin. The main bodies of island arcs are covered by Upper Triassic strata in angular unconformity.