(changchun university of science and technology, Jilin 130026)

Ehara Sachio (Yukio Kawahara)

(Department of Engineering, Kyushu University, Fukuoka, Japan)

huiping xu

(changchun university of science and technology, Jilin 130026)

From west to east along the Manzhouli-Suifenhe geoscience section, the heat flux changes as follows: Getu Mountain in Wengzhong, southwest of Manzhouli, which belongs to Ergon terrane, is 30 MW/m2; The average heat flow value of Hailaer Basin 18 is 59 MW/m2; The average value of three measured values in Duobaoshan area of Daxing 'anling terrane is 40mW/m2；. . The average value of 9 heat flows in Songliao Basin is 70 MW/m2. 47mw/m2； in Fujin area of Jiamusi terrane; The average value of three measured values in Jixi Basin is 54mW/m2. The results show that the heat flow value in the basin is high, while the heat flow value in mountainous areas and paleoterranes (Ergon terrane and Jiamusi terrane) is low. Along the geoscience section, the heat flow value has a good corresponding relationship with the Moho surface and the buried depth of high conductivity layer in the crust and upper mantle. According to the theory of Cermak and Rybach, based on refraction data, the conversion from P wave velocity to heat generation density is calculated. The calculated results are used to estimate the heat flow components of crust and mantle. This result also explains the difference of mantle heat flow along different topography of this profile. The mantle heat flux changes from west to east: Ergon terrane is 23mW/m2, Hailaer basin is 33mW/m2, Daxing 'anling region is 33mW/m2, Songliao basin is 50mW/m2 and Jiamusi terrane is 25mW/m2. This shows that the mantle heat flux of Gouel Gong and Jiamusi terranes is very low, while that of Songliao Basin, Hailaer Basin and the central Daxing 'anling Mountains is very high. It can be asserted that the difference of thermal structure between crust and upper mantle in different terranes in profile domain leads to the change of heat flow distribution. The calculation results show that the mantle heat flow and the upper and lower parts of 10km layer in the crust have different contributions to the surface heat flow.

Geothermal mantle, geothermal structure, terrane structure

1 Introduction

The heat flow profile obtained in this study is almost parallel to GGT profile from Manzhouli to Suifenhe in northeast China. These heat flow data can be used to determine the thermal structure, thermal evolution and deep dynamic process in this area, and can also be used to explain the structure of the crust and upper mantle.

Heat flux represents the heat flux released through the crust and surface per unit area and unit time. The magnitude of heat flow is closely related to deep thermal process, deep dynamic process and the structure of crust and upper mantle. The study of heat flow distribution can not only clarify the thermal structure and process of the crust and upper mantle, but also reveal the causes of geological structures, especially basin structures. This study also provides constraints for determining the paleogeothermal of the basin related to oil and gas development, and provides important data for the development and utilization of geothermal energy in this area.

Temperature measurement of well 2

2. 1 Jintagetushan area near Manzhouli

The temperature measurement in this area was carried out in two metal exploration wells (No.650 1 and 6502), which have been put on hold for several months after drilling, so it can be considered that the temperature in the wells is close to equilibrium. The maximum temperature measurement depth of 650 1 well is 120m, the linear temperature gradient section is between 70 ~ 120m, the geothermal gradient is 1.00℃/ 100m ... The maximum temperature measurement depth of well 6502 is 70m, and the linear temperature gradient section is 60m. The distance between the two wells is only about 50m, and the wellhead height difference is 10m, so the depth of the temperature linear gradient section between the two wells is almost equal.

2.2 Duobaoshan Copper Mine in Nenjiang District, Heilongjiang Province

The temperature was measured in six exploratory wells. Because it took a long time (about 10 years) after completion [5], these wells completely reached the equilibrium temperature, so they are ideal drilling holes for heat flow measurement. Well numbers are ZK757, ZK709, ZK8 19, ZK7 16, ZK856 and ZK842 respectively. The maximum temperature measuring depths of the above wells are 90 meters, 235 meters, 70 meters, 80 meters, 370 meters and 400 meters respectively. The initial depth of the linear slope section is 30 ~ 40m. The obtained geothermal gradient is between1.10℃/100m and1.40℃/100m. See figure 1 for the temperature-depth curves of wells ZK709, ZK856 and ZK842.

Fig. 1 650 1 6502, ZK842, ZK856, ZK709, water 2, 90- water 13, 93- 156.

2.3 Jixi Basin, Heilongjiang Province

Many exploratory wells are drilled in this area every year, among which 90- water 13, water 2 and 93- 156 wells are selected for geothermal survey. Well 90- water 13 has been drilled for several years, and well water 2 has been put on hold for three months. Therefore, it can be considered that the well temperatures of these two wells are in equilibrium. The stability time of well 93- 156 after drilling is only 55 hours. The maximum temperature measurement depths of Well 90- Water 13, Well Shui-2 and Well 93- 156 are 4 10m, 390m and 500m respectively, and the temperature linear gradient profiles are170 ~ 370m,/Kloc-0 respectively. See Figure 1 for the temperature-depth relationship of Well 90- water 13, Well Shui-2 and Well 93- 156.

3 thermal conductivity measurement

Four core samples were taken from Manzhouli 650 1 well, and 8, 5, 5, 3, 4 and 5 cores were taken from ZK842, ZK856, ZK525, 93- 15, 88- Shui4, Shui2 and 93- 156 wells respectively. The thermal conductivity data of these core samples were measured by the annular heat source method in the geothermal laboratory of the Institute of Geology, Chinese Academy of Sciences. The results are summarized in the table 1.

Table 1 core thermal conductivity measurement results

sequential

3. Determination of1heat flux value

The heat flow value is calculated by the following formula

Lithospheric structure and deep action

Where q is heat flow (mW/m2), k is thermal conductivity [w/(m℃)], and dT/dz is temperature gradient (C/ 100m). The temperature gradients of linearly changing geothermal sections of wells 650 1, ZK842, ZK856, ZK709, 90- water 13, Shui2 and 93- 156 are10/06, respectively. 1. 1℃/ 100m，3.7℃/ 100m，4.3C/ 100m，2.9℃/ 100m。 Using the thermal conductivity measured above, the geothermal flow is calculated by formula (1). The calculation results of heat flux are as follows: 650 1 well 30 MW/m2, ZK842/m2, ZK8561m2, ZK709/m2, 90- water 13, 57mW/m2 and Shui2. The core thermal conductivity data of well ZK709 adopts the data of well ZK525, which is only 200 meters away.

Along the GGT profile, Hailaer Basin [5] and Songliao Basin [12, 13] have 8 and 10 heat flow values respectively. Table 2 lists all the above heat flux values. The heat flux distribution is shown in Figure 2.

3.2 Calculation of Vertical Distribution of Endogenous Heat Rate in Crust

In order to establish a geothermal structure model from heat flow data, the author discusses the statistical relationship theory between seismic wave velocity and heat generation rate proposed by Cermak [2 ~ 4] and Rybach[9]. According to this theory, the author calculated the conversion of refraction P wave velocity to heat generation rate. The calculated results can be used to estimate the mantle and crust components of the heat flow in the earth.

In five different regions, VP-A relationship is used for conversion calculation. They are the Getushan area of Jinta, Hailaer basin, Duobaoshan area, Anda and Jixi basins near Manzhouli (Figures 3, 4, 5, 6 and 7).

Table 2 compilation of heat flow data in cross section and its vicinity

Note: The data in brackets refer to the number of samples.

Figure 2 Distribution of heat flow measuring points (△)

Fig. 3 transformation between seismic wave velocity and heat generation rate in urn getushan area.

Fig. 4 Conversion between seismic wave velocity and heat generation rate in Hailaer Basin

Fig. 5 seismic wave velocity-heat generation rate conversion in Duobaoshan area

Fig. 6 Transformation diagram of seismic wave velocity-heat generation rate in Anda area

Fig. 7 Transformation between seismic wave velocity and heat generation rate in Jixi Basin

4. Thermal structure of crust and upper mantle

4. 1 equilibrium one-dimensional thermal structure

Using the one-dimensional equilibrium heat conduction equation, the temperature and heat flux components can be obtained, as shown in Table 3.

Table 3 Mantle Heat Flow and Other Parameters

4.2 Two-dimensional equilibrium thermal structure

We know that two-dimensional finite element simulation is a powerful tool to study the thermal structure of the crust and upper mantle, and the study of two-dimensional temperature distribution in GGT profile is no exception. The only difference is the parameters used in the calculation. Due to the uncertainty of kinematic parameters of the whole Eurasian plate, the Pacific plate and several landforms on the profile, such as plate convergence speed, fault movement speed, erosion rate, plate shortening, thickening and stretching, the two-dimensional finite element simulation is limited to steady-state conditions.

Two-dimensional finite element simulation is mainly used to reveal the two-dimensional thermal structure of the crust and upper mantle. According to the structural model obtained by geological and geophysical methods, a simplified calculation model is established. The stratification in the simplified model is based on seismic refraction and reflection layer, sedimentary layer, crystalline basement and Moho surface. Different terranes (Ergon, Daxing 'anling, Jiamusi and Xingkai terranes) and basins (Hailaer and Songliao basins) are considered.

The two-dimensional finite element equation is

Lithospheric structure and deep action

Where p is density, c is specific heat capacity, κ is thermal conductivity, and a is heat generation rate. If the steady state is considered and the temperature does not change with time, the equation is simplified as follows

Lithospheric structure and deep action

This formula can also be expressed by minimizing the following functional:

Lithospheric structure and deep action

Where I is the energy function, S is the study area, τ is the boundary of the area, qn is the heat flux across the boundary, κ is the thermal conductivity, and A is the heat generation rate. According to these equations, if κ, a and boundary conditions are known, the temperature distribution can be obtained by calculation. The result is shown in Figure 8.

Fig. 8 Vertical temperature distribution in Manzhouli-Suifenhe section

Unit of isoline in the figure:℃

5 Conclusion and discussion

The heat flow changes from west to east along the profile as follows: the Getushan area in the urn southwest of Manzhouli belongs to Ergon terrane, with an area of 30mw/m2；; The average heat flow value of Hailaer Basin 18 is 59 MW/m2; The average value of three heat flow measurements in Duobaoshan area of Daxing 'anling terrane is 40 MW/m2. The average value of 9 heat flows in Songliao Basin is 70 MW/m2. The beautiful terrain of Jiamusi is 47mw/m2；; The average value of three measured values in Jixi Basin is 54mW/m2. The variation of heat flow along the cross section is shown in Figure 9. It has been recognized that the measurement of heat flow is limited by the borehole distribution available for temperature measurement. The heat flow values in Daxing 'anling and Zhangguangcailing areas near this section are scarce, so the heat flow values of this section are indicated by dotted lines in Figure 9. The basin has a high heat flow value, while the mountain area and paleoterrane (Ergon and Jiamusi terrane) have a low heat flow value.

The heat flux density is closely related to the buried depth of Moho surface. The general rule is that high heat flux value corresponds to shallow Moho depth [1]. The Moho surface of this profile is obtained by refraction seismic exploration [7], which is about 40km deep in Ergon terrane in the west, 37km deep in Hailaer basin, 33km deep in Songliao basin and 39km deep in Jiamusi terrane in the east. The above heat flux is directly related to the buried depth of Moho (Figure 9). These relationships are also easy to find in other parts of China [6].

The heat flux density is also closely related to the buried depth of the crust high conductivity layer (CHCL) and the upper mantle high conductivity layer (UMHCL). This relationship is shown in Adam's empirical formula: h=h0q-a, where h is the buried depth of high conductivity layer, q is the structural heat flow value, and h0 and exponent a are the parameters representing the structural properties of a certain area. Fig. 9 also shows the change of buried depth of high conductivity layer in crust and mantle obtained by magnetotelluric sounding. The fluctuation of heat flow value in Daxing 'anling and Zhangguangcailing areas, which lack heat flow measuring points, is constructed by the change of Moho surface and high conductivity layer buried depth in the crust and mantle.

Obviously, there are obvious differences in heat flow distribution between Songliao basin and Hailaer basin. The heat flow in Songliao basin is higher than that in Hailaer basin, and exceeds the global average (63mW/m2)[8]. This means that the formation mechanism and structural characteristics of the two basins are very different. The cause of high heat flow in Songliao Basin is not only related to Moho surface and upper mantle uplift, but also related to the following three factors [13]. Firstly, Caledonian, Hercynian and Yanshanian granites are widely distributed in the basement of Songliao basin, with high heat generation rate; Secondly, Songliao Basin is a part of the Pacific Rim Rift System in eastern China, and it is a rift-depression composite basin, and the extension of its crust leads to the strengthening of thermal activity. Thirdly, Songliao Basin belongs to a closed flood detention basin, with no drainage area, and the groundwater flows slowly, with an average flow rate of only 6. 1mm/a, and a lot of heat is not easy to be lost, especially because of the large-area thick mudstone formed by the rapid invasion of lakes, which has good heat collection and heat insulation performance, so the heat energy from the deep is well preserved.

Fig. 9 Variation and geological structure of geothermal heat flow and mantle heat flow along the profile.

F1-Delgan fracture; F2- Nenjiang fault; F3- Chiayi fault; F4- Mudanjiang fault; F5-Dunmi fault

The calculation results also show that the magnitude of mantle heat flow is different in different terrane tectonic units in the profile domain. From west to east, its value changes as follows: Ergon terrane is 23mW/m2, Hailaer basin is 33mW/m2, Daxinganling region is 33mW/m2, Songliao basin is 50mW/m2 and Jiamusi terrane is 25mW/m2. It can be seen that the mantle heat flux of ancient terranes such as Ergon and Jiamusi is very low, and that of Songliao Basin is very high, while that of Hailaer Basin and Daxinganling area is very low. Therefore, it can be considered that the difference of thermal structure of crust and mantle leads to the different distribution of geothermal flow in different structural units in the profile domain. It can be seen from the calculation results that the mantle heat flow of different terrane tectonic units and the upper and lower parts of the crust with a depth of 10km have different contributions to the surface heat flow.

Songliao Basin and Hailaer Basin, two great basin, belong to two types in profile, which are quite different from each other in terms of the shape of mantle heat flow and the thermal structure of the crust. The mantle heat flow in Songliao Basin is 50mW/m2, accounting for about 60% of the surface heat flow, while that in Hailaer Basin is 33mW/m2, accounting for about 52% of the surface heat flow. The great difference between them shows that the thermal structure of the upper mantle of the two basins is very different. The difference of thermal structure between the two basins is related to the tectonic position. According to the recent comparative study of mantle structure and plate insertion history revealed by Japanese scholars through seismic tomography [10], when the inserted "cold" plate in the Pacific Ocean descends from the upper mantle to the lower mantle, a "hot" mantle column will inevitably rise from the lower mantle to the upper mantle in order to compensate for its descending part. The rise of this "hot" mantle plume may be the fundamental reason for the unusually high heat flow in Songliao Basin. According to the thermal structure of the crust shown by the calculation results, the contribution of the upper part (22.2mW/m2) of the deep crust in Songliao Basin is much greater than that of the lower part (8.8mW/m2), while the contributions of the upper part and the lower part of Hailaer Basin are 15.8mW/m2 and 14.3mW/m2 respectively. It shows that the enrichment degree of radioactive elements in the crust of Songliao basin is higher than that of Hailaer basin, that is, the differentiation degree of acidic, basic and ultrabasic rocks in Songliao basin is higher than that in Hailaer basin. The above situation is consistent with the fact that extremely thick granite is distributed in the depth range of 5 ~ 13 km below [13] in Songliao basin.

Thanks to Academician Wang Jiyun and Researcher Shen Xianjie from Institute of Geology, Chinese Academy of Sciences for their guidance and help, and also to Professor Shi Yaolin from Graduate School of Chinese Academy of Sciences for his assistance in two-dimensional finite element calculation. In the process of completing the English manuscript, the associate professor gave warm help, and I also want to express my gratitude here.

refer to

[1]D.S.Chapman and L.Rybach Heat flow anomaly and its explanation. J. geodynamics,1985,4,3 ~ 37.

[2]V.Cermak. Crustal heat generation and mantle heat flow in Central and Eastern Europe. Tectonic physics, 1989, 159(3 14), 195~2 15.

[3]V.Cermak. Crustal temperature and mantle heat flow in Europe. Tectonic physics,1989,83, 123~ 142.

[4]V.Cermak and L.Rybach. Vertical distribution of heat production in continental crust. Tectonic physics, 1989, 159, 2 17~230.

Exploration department of Daqing Petroleum Administration Bureau. Research report on source rocks in Hailaer basin, Inner Mongolia Autonomous Region. 55438+0990。

Wook Kim, Gao Rui. Characteristics of thermal structure and crustal and upper mantle structure in eastern China. Journal of Japan Geothermal Society, 1990, 12 (2), 129 ~ 143.

Wook Kim, Yang Baojun. Geophysical field and deep structural characteristics of Manzhouli-Suifenhe geoscience section in China. Beijing: seismological press, 1994.

Li Weiguang. On the global change of the earth's heat flow. Journal of Geophysics,1970,2,332 ~ 359.

[9]L.Rybach, G.Buntebarth. Variation of thermal generation density and seismic velocity of continental lithosphere with rock types. Tectonic physics, 1984,103,335 ~ 344.

[10] Maruyama Maud, Jixiong Shenwei, Dalin Zhengxin. Plume technology. Science,1993,63 (6), 373 ~ 386.

The second regional geological survey team of Heilongjiang Province. Detailed investigation report of Duobaoshan copper belt in Nenjiang area of Heilongjiang Province, 1982.

[12] Wang Jiyun, Huang. Compilation of Geothermal Flow in Chinese mainland Area (2nd Edition). Seismogeology, 1990, 12 (4), 35 1 ~ 366.

[13] Wu Ganfan, thank you. Geothermal flow in Songliao basin. Seismogeology,1985,7 (2), 59 ~ 63.