Characteristics and Dynamic Mechanisms of the Stress Field of the Indosinian Movement in Hunan Province
For a long time,the manifestation of the Indosinian Movement and the formation age of the folds in the Upper Paleozoic cap in Hunan Province in central South China have attracted the attention of research-ers,but there are still significant differences in understanding of this.Given this,based on the author's years of research achievements,this paper has systematically summarized and explained the regional stress field characteristics and determination basis of the Early and Late Indosinian Movement in Hunan Province,and explores the dynamic mechanisms of stress field formation and other related issues of the Indochinese Move-ment,achieving the following main understandings.(1)The Early Indosinian Movement occurred in the late Middle Triassic,with significant changes in the direction of regional maximum principal stress.In the middle belt of Hunan Province,from northwestern to central Hunan and to the east part of southeastern Hunan,the di-rection of regional maximum principal stress generally deviated in an arc from NNW-near SN to NW and fi-nally to NWW;in the southwest belt,the direction changed from NW in southwestern Hunan to EW in cen-tral-southern Hunan,and then to EW in western part of southeastern Hunan;in the northeast belt,it changed from SN in northeastern Hunan to NW and NWW in eastern Hunan.The Late Indosinian Movement occurred in the Late Triassic,with the regional maximum principal stress direction of SN,and locally NNE in some ar-eas of central Hunan.(2)The compressive stress field in the Early Indosinian Movement was mainly related to the southward compression of the North China Block,the northward compression of the Simao-Indochina Block,and the northwestward compression of the Paleo-Pacific Plate.The secondary intracontinental conver-gence between various secondary blocks distributed in a NE-NNE direction,the sinistral strike-slipping of NW-trending basement hidden faults,and the obstruction of the Caledonian Yuechengling and Miao'ershan granitoids also played an important controlling role.The regional SN compressive stress field in the Late In-dosinian Movement is related to the southward compression of the North China block and the northward com-pression of the Simao-Indochina block.The NNE maximum principal stress in local areas was related to the dextral strike-slipping of the NW-trending Changde-Anren and Chenzhou-Shaoyang basement hidden faults.(3)The NW compression of the Paleo-Pacific plate might be the best dynamic explanation for the NE-trend-ing folds during the Indosinian in South China.The development degree of NE-trending folds in central Hu-nan appeared much higher than that of EW-trending folds,which could be an important piece of evidence that the former should have formed earlier than the latter.The NE-trending tectonic uplift zone from Gaoguashan to Simingshan in central Hunan was controlled by SN compression in the Late Indosinian Movement and was formed by lateral flattening and vertical stretching of the early NE-trending weak structural zone.
Early Indosinian MovementLate Indosinian MovementRegional compressive stress fieldDy-namic mechanismsSouth China blockHunan Province
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