Lithospheric long-wavelength magnetic anomalies and their geological origins:A review

Wang Jie; Yang Yanyan; Ji Fei; Luo Yuxin; Zeren Zhima; Huang Jianping; Shen Xuhui

doi:10.19975/j.dqyxx.2023-056

Abstract：At the altitude of low-Earth-orbiting satellites,most details of lithospheric magnetic anomalies ob-served near surface are attenuated,and only slowly decaying long-wavelength magnetic anomalies can be detected.Long-wavelength magnetic anomalies are generated by large-scale magnetized rocks in the Earth's crust and upper-most mantle at depths shallower than the Curie depth.Interpretation of such lithospheric magnetic anomalies has been used in geological mapping,crustal composition and structure studies,plate tectonic reconstruction,and geo-dynamics.To introduce the origin of long-wavelength magnetic anomalies at a global scale,we first reviewed satel-lite magnetic anomaly maps in early periods and calculated anomaly maps using four main lithospheric magnetic field models,including the CHAOS-7,CM6,MF7,and CSES models.Then,based on the result of the CHAOS-7 model at 500 km altitude,29 long-wavelength magnetic anomalies with amplitudes greater than 4 nT were identi-fied and their geological origins were reviewed.Among these,there were twenty magnetic anomalies over conti-nents and nine over the ocean.The long-wavelength magnetic anomalies over continental areas were mostly loc-ated in Precambrian basements related to the Archean nuclei,Proterozoic terrane,and iron-rich formations,with a few located in the orogenic background.The long-wavelength magnetic anomalies in the ocean region were all loc-ated in oceanic plateau,generally related to the breakup of Gondwana during the Cretaceous Period,and have the characteristics of thickened crust.Hence,the long-wavelength magnetic anomalies reveal a significant magnetiza-tion difference in the deep crust during crustal growth,a key issue that requires further study.Compared to satellite magnetic surveys in some other nations,detecting lithospheric magnetic anomalies by satellite started relatively late in China.The China Seismo-Electromagnetic Satellite(CSES)was launched in February 2018.It was China's first satellite designed to monitor earthquakes with multiple geophysical payloads,including magnetometers capable of measuring weak signals from the lithosphere.The Macau Science Satellite-1(MSS-1)was launched in 2023 and is specially used for monitoring the geomagnetic field in low latitudes.Furthermore,a subsequent CSES-02 satellite is planned to be launched in 2024.With the vigorous development of satellite magnetic surveys in China,it is expec-ted that progressively more Chinese researchers will pay attention to long-wavelength magnetic anomalies and pro-mote the study of their origin.