Mesozoic uplift and volcanic-sedimentary basin in Yanshan area are distributed alternately and equidistantly (Figure 4-5).
Three first-class banded uplift belts and five first-class northeast uplift belts developed in Yanshan area in Mesozoic. From north to south, the main banded uplift zones are Weichang-Harqin Banner-Fuxin North Uplift Zone, Chongli-Chengde North-Lingyuan Uplift Zone and Miyun-Qinglong-Suizhong Uplift Zone. From east to west, the main NE uplift belts are Changli-Shanhaiguan-Yiwulushan uplift belt, Qianxi-Lingyuan uplift belt, Xinglong-Zheshanzi uplift belt, Qifengcha-Weichang uplift belt and Sanyizhuang-Xuanhua uplift belt. Along the axis of these uplift zones, Archean-Proterozoic medium-deep metamorphic rock series and Mesoproterozoic-Early Paleozoic carbonate-clastic rock series are widely exposed, among which Mesozoic volcanic-sedimentary rocks are few or undeveloped, reflecting that they are mostly in uplift and denudation state in Mesozoic. At the intersection of northeast uplift belt and belt uplift belt, they combine to form a uplift area. There are depression sedimentary areas between uplift zones, and Mesozoic volcanic-sedimentary basins are developed, such as Jianchang Basin, Chaoyang-Beipiao Basin, Ningcheng Basin, Luanping Basin, Kuancheng Basin and Yuxian Basin (Figure 4-5).
J.G.Ramsay pointed out that fold structure can be quantitatively described by Fourier function. The uplift and depression zones regularly distributed in Yanshan area can also be quantitatively analyzed by similar methods, thus establishing the mathematical model of Mesozoic uplift and basin distribution in Yanshan area.
Select the center point of the superimposed uplift area at the southwest end as the coordinate origin, with the Y axis parallel to the zonal uplift axis and the east positive; The x axis is perpendicular to the y axis, and the north is positive; Y ′ axis is parallel to NE uplift axis, and NE is positive; The x' axis is perpendicular to the y' axis, and the northwest direction is positive. Let the angle between the X axis and the y' axis be α, then the following coordinate transformation relationship exists:
Gold polymetallic mineralization and its tectonic-metallogenic relationship in Yanshan intracontinental orogenic belt
Let the axial spacing of the banded uplift belt be a and the axial spacing of the ne uplift belt be b..
The strength or relative uplift height z 1 of the banded uplift zone increases sharply from north to south, which can be described by the following formula.
Gold polymetallic mineralization and its tectonic-metallogenic relationship in Yanshan intracontinental orogenic belt
NE uplift belt has the characteristics of alternating strength. Weichang-Fengning-Laiyuan uplift belt and Chaoyang-Jianping-Qianxi uplift belt are strong, while the other three uplift belts are weak, which can be described by the following formula.
Gold polymetallic mineralization and its tectonic-metallogenic relationship in Yanshan intracontinental orogenic belt
H, H and K are constants used in the fitting process, K > 1, and their values can be determined according to the characteristics of superimposed uplift areas. The intrusions in Chengde uplift area and the center of the uplift area are distributed in a nearly circular shape, which indicates that the Zhangjiakou-Fengning-Longhua uplift belt passing through this area is similar to the Zheshanzi-Chengde-Xinglong uplift belt, and can be approximately taken in this area.
Gold polymetallic mineralization and its tectonic-metallogenic relationship in Yanshan intracontinental orogenic belt
Figure 4-5 Isograms of Mesozoic Paleotectonic Geomorphology and Relative Elevation of Yanshan Intracontinental Orogenic Belt
Figure 4-5 Mesozoic paleobasin-mountain network and uplift isobath distribution in Yanshan intracontinental orogenic belt
1- Mesozoic relative elevation isoline; 2- Mesozoic sedimentary rock series; 3- Mesozoic volcanic rock area; 4— Axis of regional uplift belt
Substituting x' =-2b and x = a into formulas (4.3.3) to (4.3.5) gives:
Gold polymetallic mineralization and its tectonic-metallogenic relationship in Yanshan intracontinental orogenic belt
Assuming that the ratio of wavelength to wave height of zonal and northeast uplift is equal, then
Substitution into (4.3.6) gives:
Gold polymetallic mineralization and its tectonic-metallogenic relationship in Yanshan intracontinental orogenic belt
The superposition of uplift zones can be expressed as
Gold polymetallic mineralization and its tectonic-metallogenic relationship in Yanshan intracontinental orogenic belt
According to the geological map of1:500,000, a= 18.5cm, b= 17cm and α = 4 1.5 are measured. Substituting a and b into equation (4.3.7) gives k=2.50. Substituting these parameters into equation (4.3.9) gives the following results.
Gold polymetallic mineralization and its tectonic-metallogenic relationship in Yanshan intracontinental orogenic belt
Gold polymetallic mineralization and its tectonic-metallogenic relationship in Yanshan intracontinental orogenic belt
Z is the relative uplift height of Yanshan area in Mesozoic. According to formula (4.3. 10), the elevation contour of Mesozoic relative uplift in the whole area is calculated (Figure 4-5). As can be seen from the figure, Mesozoic volcanic-sedimentary rock series are mainly distributed in the depression area with z≤0 and the uplift area with Z ≥ 1; Depression center z ≤- 1, uplift center z≥2. The actual Mesozoic basin shape is in good agreement with the depression area shape of z≤0 or Z ≤- 1. Equation (4.3. 10) is a mathematical model describing the distribution of Mesozoic uplift and depression in Yanshan area.