| In recent years, with the rapid development of China’s economy which causes a large amount of mineral resources to be consumed, especially the shallow mineral resources have been mined。In order to maintain the growth momentum of the economy of our country, it is urgent to solve the problem of the shortage of resources, so the deep prospecting has gradually become a focus in resource exploration. As an important metallogenic belt in China,the Liao-Ji belt has a long and complex evolution history, with deep mineralization favorable conditions. Therefore, it is significant to study the deep geological structure of the Liao-Ji rift zone to deepen the understanding of geological characteristics of the North China and to find the deep mineral resources. Previous research on Liao-Ji rift mainly concentrates in the surface geology, and lacks of understanding of the deep geological structure, which in a large extent restricts the comprehensive understanding of the geological characteristics of the study area and deep metallogenic prediction.This thesis makes a systematic study on the deep geological structure of the Liao-Ji rift in Kuandian-Huanren area(including Kuandian County, Benxi County, Huanren County, the western Ji’an City).Based on the results of previous studies, the author combines the geology with non-seismic geophysical method, collected the previous geological data in the study area, analyzed the regional gravity, magnetic and non-seismic geophysical profiles(measured high-precision gravity and magnetic, measured MT).Based on the rock physical parameters, the deep geological structure of the Liao-Ji rift was revealed. The author established the deep geological framework of the Liao-Ji rift and Longgang block, determined the location of the tectonic boundary between the Longgang block and the Liao-Ji rift, further deepened the understanding of the formation and evolution history of the Liao-Ji Rift, discussed the basement structure and composition of Liao-Ji Rift, revealed the three-dimensional spatial distribution and geometric shape of the main stratigraphic units, the rock masses and the faults in the Liao-Ji Rift, and established the three-dimensional geological model of Huanren-Kuandian area. The main contents of this paper are as follows:(1) Based on the gravity inversion interpretation of the 10 main sections and interpretation of the 10 measured MT profiles in the study area, the author has established the deep geological framework of the Liao-Ji Rift and the Longgang block in the study area.The main body of the Longgang Block features a two-layer structure with the Archean metamorphic basement covered by Neoproterozoic-Paleozoic sedimentary rocks of the Taizi River Basin. The basement is mainly composed of Neoarcheantonalitetrondhjemite-granodiorite(TTG) gneiss and relics of supracrustal rocks. The rock formation in the Liao-Ji Rift was subjected to intense fold.In the vicinity of the tectonic boundary between the Paleoproterozoic Liao-Ji Belt and the Longgang Block, underneath the Liaohe Group is the Archean crystalline basement. And in the central region of Liao-Ji Rift, underneath the Liaohe Group is Ancient Proterozoic granite.(2) A comparison between gravity and aeromagnetic slice maps at different depths combined with regional geological data reveals the deep geological structure of Benxi-Huanren area and provides important information for study of the deep geological evolution process of Benxi-Huanren area. Yanshanian granitic pluton is widely distributed in this area, and tends to be continuous towards depth.According to “m” shaped magnetic anomaly in Anshan area and also the regional geological information, it is inferred that this special distribution pattern of magnetic anomaly is resulted from folding of Archean iron-bearing formation.(3) Euler deconvolution was applied to the gravity and magnetic data of the whole area. After that, the extension depth and the tendency of the main structural lines in the study area were obtained.Through the comparison with the regional geological data, it is found that these tectonic lines are in agreement with the main fractures or fit the boundaries of the rock masses.For example, the boundary of the Balidianzi rock mass, the position of Hanling-Pianling fault, Erhulai fault, Taipingshao fault and so on; in deep underground, the Cretaceous granites in eastern Kuandian are contiguous to expand the trend.(4) Employing non-seismic geophysical data(e.g., gravity data and magnetotelluric soundings), existing geological data, and the differences in physical properties between the Liao-Ji Belt and the Longgang Block, we clarified the spatial distribution of the tectonic boundary, and characterized the geological bodies at different depths on either side of the boundary. The results indicate that during the early period of formation of the Liao-Ji Belt, a basin-controlling boundary fault developed that constituted the original tectonic boundary between the Liao-Ji Belt and the Longgang Block. This fault extended from Shuangtaling to Sandaoling, Lian Shanguan, Dawanggou, Balidianzi, and Erhulai to Guaimozi, following a roughly east-west trend. And it is a normal fault which suffered from a strong transformation later. In some areas, the Mesozoic rift basins were developed; some regions were occurred early Cretaceous magmatic intrusion.(5) This study deepens the understanding which is the tectonic evolution process for the Liao-Ji Rift from the perspective of deep geology. The Longgang and Nangrim blocks originated from the same micro-block. After Paleoproterozoic rifting, the micro-block began to constantly stretch, following this, the Liao-Ji Belt developed into an ocean basin in its eastern segment. Finally, the back-arc basin closed through bi-directional(southwards and northwards) subduction and collision, and formed the rift zone.(6) The author established the three-dimensional geological model for the area of Kuandian, Huanren and the western region of Ji’an and determined the deep geological structure, it can be divided into several pieces: 1 the changes in the depth of the Liaohe Group’s bottom is relatively large. From the southern Hongshi, to the northern Daxicha to Taipingshao, Budayuan and Xialuhe area, the depth increases; the depth of Hongshi, Daxicha area is less than 1000 m, the average depth of Taipingshao, Budayuan and Xialuhe is more than 4000 m, and the depth of the northern Budayuan area and Mesozoic basin is up to 7200 meters. 2 the depth of the Liaohe Group bottom boundary is less than 2000 meters, that is closed linear folds in Kuandian area. The area has experienced a strong uplift, that can be said to be the deep deformation results of the Liao-Ji Rift. 3 the depth of Saima alkaline rock mass bottom boundary is shallow, which indicates it was suffered from a strong denudation. 4 It can be supposed that the complex fold is formed by a complete syncline, near Pingdingshan and Dasiping County. 5 It reveals that the Changdian rock mass has a larger distribution range in the deep, the shape of Changdian rock mass is a column whose upper part is wide and lower part is narrow, the western part of the rock mass has a large scale underground and shows lower density which the rock mass is speculated to be adamellite.The rock mass has a branch in the east and the maximum depth of the rock bottom is up to 7000 m. |
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