The Research Of The Main Fracture Structure’s Feature In The North Part Of Xiangshan Volcanic Basin

Xiangshan volcano basin of the early cretaceous epoch locates in the superposition part between the near east-west trending Gan-Hang uranium metallogenic belt which belongs to the volcanic-type and the north-south trending Dawang mountain-Yushan granitic uranium metallogenic belt. While it developed in the central part of the near east-west tangang-Xiangshan duplex anticline which is composed by the metamorphic rock of Qingbaikouan system of the Xuefeng-Caledonian period. The thesis is based on the 3d geological survey of the Xiangshan Volcano Basin of the China Geological Survey. On the basis of data including the main lithostratigraphy and stuctural feature in Xiangshan volcano basin and so on, the main structural characteristics in Xiangshan volcano basin is studied systematicly through the refined field structural section measurements and outcrop investigation, route exploration, trench profiles, joints statistical analysis, combined with the analysis of drilling data in recent years, especially the north part of Xiangshan. The thesis mainly achieves the following results and understanding:(1) Xiangshan volcano basin is based on the lightly metamorphosed basement of Qingbaikouan system. of the Xuefeng-Caledonian period. The near east-west fold in the basement of the metamorphic rock is developed in the north-south trending tectonic movement took place in Xuefeng-Caledonian period, which can be divided into three parts, namely Peifang overturned syncline, Tangang-Xiangshan complex anticline and Nanmeifeng syncline. Xiangshan volcano basin is located in the eastern central part of the Tangang-Xiangshan complex anticline.(2) There develops three ne-trending main faults in the north part of Xiangshan volcanic basin, which are Zoujiashan-Shidong fault, Baqian-Shimashan fault and Zoujia-Bushui fault. These ne-trending faults are the main structure features and the faults had been experienced multi-stages tectonic activities which is influenced by Dexing-Suichuan deep fault.The multi-stages tectonic activities embodied the sinistral strike slip activities in Caledonian to Yanshanian, the extension activities in the late Yanshan, the regional squeezing action in Himalayan.(3) The near east-west trend faults in north part Xiangshan volcano basin is a series of faults with similar feather, high angle, south dipping reverse fault. The time of the formation of these faults is earlier than that of the early Cretaceous volcano activity and can be traced back to the Caledonian. These faults may generated during the formation of the near east-west duplex anticline and had experienced multi-stages tectonic activities. These faults may have experienced the following evolutionary stages:These faults may have formed in the process of the complex fold in the basement of the volcano basin. The fault strike and the hinge line of the fold was the same. They as the low-order fracture of ne-trending main faults revived with the other faults beside of them in the late Caledonian. With the effect of sinistral strike-slip of the ne-trending main faults, the near east-west trend faults closed by them became into the thrust faults.Deep crustal magma upwelling due to the large-scale magmatic activity and it squeeze the north part of the study area in the mid of Yanshanian. The near east-west trend faults of the edge of the volcano basin once again the activity with the evolution of the Suichuang-Dexing fault. The magma invaded in the fracture and into the wall in the volcano activity.These near east-west trend faults in north part Xiangshan volcano basin were revived with the regional main faults beside of them by effect of the sinistral strike-slip or extension in the late Yanshanian to Yanshanian.