Abstract:

he Chagan sag developed on the ancient orogenic belts near the northwestern margin of North China Plate, which was a postorogenic extensional collapse basin. Both of the “Maodun Intrusion” and “Maodong Fault” in the southeastern Chagan sag primarily formed before the Cretaceous period, and belong to the component parts of the Chaganchulu deep fault zone beneath Chagan sag. The “Hantamiao subsag” that was once considered to be a structural unit of Chagan sag, mainly consists of remnant preCretaceous strata, but Early Cretaceous strata developed in the faulted basin. The structural framework was controlled by fault zones with variant scales in this sag. Generally, the structural styles can be divided into four primary patterns including extensional structures which were dominant, compressional structures, inversion structures, and the structures with strikeslip component. During the Cretaceous to Cenozoic era, the tectonic evolution of Chagan sag had underwent five stages,namely extensional faulted basin generation, development, weakly extensional faulteddepressed transition, steady depression, and compressional reform stages.

Key words: Chagan sag, structural framework, structural style, evolution