Towards improved knowledge of geology and global thermal regime from Swarm satellites magnetic gradient observations

Gradients of magnetic field have higher spatial resolution than the fields themselves and are helpful in improving the resolution of downward continued satellite magnetic anomaly maps (Kotsiaros et al., 2015, Geophys. J. Int.; Sabaka et al., 2015, Geophys. J. Int.). Higher spatial resolution and fidelity of the magnetic field downward continued to the Earth’s surface translate into improvements in the interpretation of anomalies for recognition of geologic variability and tectonic processes (e.g., recognizing details of geologic provinces, anomalous seafloor spreading patterns, etc., that can help understand the evolution of the Earth).

Magnetic anomalies have sensitivity to thermal variations in the Earth’s lithosphere through the phenomenon of Curie temperature of ferromagnetic minerals. The response of the bottom of magnetization in the Earth’s crust/lithosphere is primarily observed in the long wavelength magnetic field up to at least 500 km (and sometimes longer).

The Curie temperature depth can also be used to better map the thermal structure of the lithosphere because it is possible to theoretically include the Curie depth constraint in the derivation of the one dimensional geotherm (Ravat et al., 2015, in review). Despite having global set of observations from POGO, Magsat, Ørsted, CHAMP, and Swarm satellites (altitude > 400 km), preservation of intermediate wavelengths from about 100 to 375 km proves challenging (known as the “spectral gap”).

Since the gradients of magnetic field have higher spatial resolution than the fields themselves, they are helpful in improving the coverage in the spectral gap. East-West and North-South (along orbit) gradients from Swarm magnetic field satellites provide an opportunity to examine the improvement in the anomaly coverage in the spectral gap and its effect on the interpretation, particularly the derived Curie depths and the thermal variation of the lithosphere.

We examine the inaccuracies in anomalies and also their resulting interpretation using the U.S. aeromagnetic data where a full spectrum magnetic anomaly coverage is available (Ravat et al., 2009, USGS open files report OF09-1258) as a result of the availability of NURE data which were corrected with the comprehensive model of the magnetic field (CM4, Sabaka et al., 2004, Geophys.

J. Int.). We specifically compare various levels and types of corrected data sets: uncorrected original North American Magnetic Anomaly Map compilation (ca. 2002), the original compilation corrected with satellite-altitude data sets, and Swarm constellation gradient corrected fields over the U.S. Using this U.S. study as a test, we examine the possibility of improving the spectral coverage in many regions of the world where anomalies and their interpretations are still affected by the spectral gap.