The Three-dimensional Geometry Of Mesozoic Intrusive Rocks And Its Genetic Significance

There are many types of Mesozoic intrusive rocks of multiple periods in the eastern part of Liaoning,ranging from a wide range of acidic granite bodies to extremely special-distributed basic-ultrabasic rocks and from macrobatholith to small-scale intrusive dyke.The form of rocks varies from regular shape(such as an ellipse and dumb-bell shape)to irregular shape(for example,multiple-brunch shape).There are also alkaline rock bodies from the mantle and composite reverse-zone shaped intrusive bodies.All of these laid the foundation for studying the three-dimensional(3D)geological structure and emplacement mode of intrusive bodies,and provided conditions for exploring the evolution of crust and mantle in the lithosphere.Previous studies of intrusive rocks have focused on petrography and petrochemistry,and there have been few studies on the three-dimensional geometry of intrusive rocks.Since the information provided by surface geological work is not comprehensive,in order to gain a deeper understanding of the formation age,formation mode and significance of regional revolution,deep geological research must be carried out.The 3D model of the intrusive rock visually reflects the deep information and provides conditions for solving geological problems.This paper collects regional geological data,geochemical data,geophysical data(such as regional gravity and magnetic data and measured high-precision gravity magnetic profile data).Techniques including 3D density inversion and combined gravity and magnetic inversion are used to reveal the three-dimensional geometric shapes of Mesozoic intrusive rocks in Benxi-Dandong of eastern Liaoning to explore the relationship between the 3D geometry of the rock and the emplacement mechanism and mineralization.The main research objects of this paper are the Saima alkaline rock mass,the Xuetun basic-ultrabasic rock mass,the Shimiaozi diorite rock mass,the Hanjialing rock mass,the Dixiongshan rock mass,the Balidianzi rock mass and the Changdian rock mass.In the research process,a reconstruction method for the 3D geometric shape of the intrusive rock is proposed.Different emplacement mechanism and different geotectonic environment during the formation period lead to different geometrical forms of intrusive rock masses,whose indicated prospecting significance is also different.Studying the 3D geometry of the Mesozoic intrusive rock mass in this area is of great significance for analyzing its emplacement mechanism,studying the tectonic setting,and speculating favorable metallogenic areas.The main conclusions are as follows:1.A method for 3D geometric reconstruction of intrusive rock mass is proposed.Taking 3D density inversion as the core technology,a variety of constraints are introduced in the formation of the 3D model of the rock mass,including the magnetotelluric sounding profile to determine the depth and boundary shape of the rock mass,the boundary identification method to determine the horizontal boundary shape of the rock mass,and the Euler deconvolution method to determine the buried depth of the rock mass,etc.Finally,the existing data is used to verify the accuracy and reliability of the rock mass morphology.2.The 3D geological structure model of the main Mesozoic rocks in the Benxi-Dandong area of eastern Liaoning was constructed,and the 3D geometry of the intrusive rock was classified.It is mainly divided into two categories: irregular shape,represented by Saima alkaline rock mass;regular form,including thick plate shape,represented by Balidianzi rock mass,saddle shape,represented by Shimiaozi rock mass;and the regular shape also contains ellipsoid-like which is represented by Hanjialing rock mass and Xuetun rock mass,with its subdivision divided into a pear shape and a comma shape.3.The relationship between the geometry and emplacement mechanism of the Mesozoic rock mass is clarified,and the distribution law of the Mesozoic rock mass is summarized and analyzed.The emplacement mechanism of intrusive rock mass is mainly divided into two categories,including active emplacement and passive emplacement.When the intrusive rock mass is actively emplaced,the original 3D geometry is closer to a spherical shape(such as inverted water droplets and balloon shape).When the intrusive rock mass is passively invaded,its original 3D geometric form is divided into two categories: regular and irregular.The regular shape is closer to the long ellipsoid and plate shape with its long axis direction consistent with the fracture direction;the irregular shape is characterized by multiple branches with the trend is controlled by small faults.If the rock mass is irregular and has multiple branches,the rock mass is very likely to be passively invaded.The shape of the rock mass is regular,such as the ellipsoidal shape,which indicates that the rock mass is very likely to be an active invasion.If the rock mass is exposed in the form of rock foundation,it may be a model of passive wall emplacement.The shape is more inclined to erect thick plate.The location of the rock mass indicates the existence of deep and large faults.The propagation of the intrusive rock mass is consistent with the direction of deep and large fault.4.The influencing factors of 3D geometric shape of the intrusive rock mass are discussed in this paper.The main controlling factor of the 3D geometry of the intrusive rock mass is the degree of magmatism,and it is also affected by the magma emplacement stage and final location.When the magma activity is severe and the magma material is sufficient,the original shape of the intrusive rock mass is relatively regular,and vice versa.The 3D geometry of intrusive rock formed by a single intrusion is more regular than multi-stage intrusion.If the rock mass is invaded into the stratum,the shape is relatively regular,while the geometric is irregular as the magma invaded into the rock mass.5.The analysis of the deep mineralization of gold,lead,zinc and jade deposits in the Mesozoic intrusive rock mass is proposed.In the process of emplacement,whether the magma is actively or passively invaded,the surrounding rock will be transformed by thermal power,leading to contact thermal deformation or hydrothermal metamorphism,which will provide favorable conditions for mineral formation and mineral accumulation.This paper predicts the existence of concealed minerals in the Changdian-Kuandian area.