Magnetic Imaging of the Curie Isothermal surface under Guangdong Province and its application in Guangdong geothermal modeling

Crustal rocks lose their magnetization at the Curie point temperature about 800K. Hence, the Curie isotherm is the bottom of the magnetized crust, which reflects the thermal state of the lithosphere rather than geological structure. A geothermal anomaly is obvious in Guangdong province. We study the spatial variation of the depth of the Curie isotherm under Guangdong province using aeromagnetic data. We employ the continuous model method and build a geothermal model with the Curie isothermal as a constrain condition to study the thermal state of crust under Guangdong province. The Guangdong Geology Bureau conducted an aeromagnetic survey over Guangdong province with a resolution of 0.02°×0.02°. The data cover the whole Guangdong region extending from 20.14°N to 25.64°N latitude and from 109.52°E to 117.22°E longitude, over 50,000 measuring points. After given the average magnetization and the average depth, undulations of Curie isotherm is expressed as a Fourier series using the linear approximate inversion formula of Peters (1949). The Fourier coefficients of the undulations of the Curie isotherm are obtained using the least square method. The result shows that average depth of Curie isothermal surface under Guangdong province is 18km, and the undulation is over 9km.Average depth of the Moho is 32km, which is well below the Curie isotherm. In Shaoguan, north of Guangdong province, both the Curie isotherm and the Moho surface are deeper. This is consistent with the low heat flow in this region, and can be interpreted as indicating thick lithosphere. In contrast a significantly shallower Curie isotherm and Moho are observed in Guangzhou. This is consistent with high heat flow in this region and can be interpreted as indicating thinner lithosphere due to the heating by a mantle plume. The Curie isotherm can indicate the thermal state of the deep crust and is a very powerful constraint for geothermal modeling.We built a convective geothermal model of Guangdong province with the Curie isotherm as a constrain condition and got the mantle heat flow.