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A series of Jurassic-type folds have continuously developed in the Mesozoic from the Sangzhi-Shimen area in northern Hunan. The analysis of the fold superimposition characteristics is of great significance to explore the deformation period and deformation mechanism of the Sangzhi-Shimen complex oblique folds, and also for the theoretical study of fold deformation controlled by faults. Based on the measurement of geological structure section and analysis of fold superimposition characteristics in Sangzhi-Shimen area, two fold structures in Indosinian and early Yanshanian were identified. The low-angle unconformity contact between the Jurassic and the Middle Triassic in the study area, and the high-angle unconformity contact between the Cretaceous and the Pre-Cretaceous reflect two deformation events of Indosinian and Early Yanshanian movement. It can be further inferred that the folds in the Sangzhi-Shimen area can be divided into two phases: the Indosinian movement and the early Yanshanian movement.The Indosinian fold axial trace mainly showed NEE to near EW; the early Yanshanian fold axial trace can be divided into two groups, one is NEE-near EW, the other is NNE. Two groups of early Yanshanian folds and pre Indosinian folds are superimposed to form two types of superposed folds, the enhanced type and the oblique limited type. The former is controlled by the inherited activities of the Indosinian NEE-near EW reverse fault; the latter is controlled by NNE trending reverse fault, which formed by NWW trending regional compressive stress in early Yanshanian, and it is limited by the pre NEE-near EW trending structure.This deformation mechanism well explains that the fold axis and thrust fault in the study area have no east or Southeast inclined polarity.

Changde-Anren fault is a large NW-trending fault in eastern Hunan Province.Based on a large number of basic geological data, this paper summarized the segmental characteristics of the fault; according to the oringin and distribution of Indosinian granite in the fault zone, the paper suggests that the activity of the fault in the main episode of Indosinian movement in the Late Middle Triassic was segmented.According to the structural characteristics of the fault and its two sides, the exposed strata and magmatic rocks, the Changde-Anren fault can be divided into four segments such as Anren-Hengshan segment (Ⅰ), Xiangxiang segment (Ⅱ), Taojiang segment (Ⅲ) and Changde-Shimen segment (Ⅳ), between which are NE-trending deep faults that cut through the deep crust and even the mantle.The NE-trending deep faults were mainly formed in Caledonian movement with sinistral strike-slipping, and cut the Changde-Anren fault into several disconnected segments, which resulted in the segmentation of the movement in Mesozoic of the Changde-Anren fault.In the region, the Late Triassic granites are mainly S-type granites formed by deep crustal melting in a post-collisional environment.The distribution characteristics of Late Triassic granites in the Changde-Anren fault indicate that the activity of the fault in the main episode of Indosinian movement is obviously segmented: there occurred shearing of the Xiangxiang segment of Changde-Anren fault in the deep part in Middle Triassic Indosinian movement, when the movement amplitude, shear strength and corresponding warming effect decreased from the middle to the end of the segment for the end restriction, which caused that the decompression-melting of deep crustal in Late Triassic only occurred in the middle part of Xiangxiang segment, and the corresponding granites were exposed in the middle and northern sections of Xiangxiang segment.This structural-magmatic mechanism is also reflected in Anren-Hengshan segment and Taojiang segment.The segmental movement of the Changde-Anren fault in Indosinian is a "passive" segmental movement after the first penetrating fault was divided into several segments by the NE-trending deep fault, which is different from the general "active" fault segmental movement or segmental growth with many small faults occurring, expanding and finally being connected into a large fault.