Mapping and Interpretation of the Lithospheric Magnetic Field

Abstract

We review some of the controversial and exciting interpretations of the magnetic field of the earth's lithosphere occurring in the four year period ending with the IAGA meeting in Sopron in 2009. This period corresponds to the end of the Decade of Geopotential Research, an international effort to promote and coordinate a continuous monitoring of geopotential field variability in the near-Earth environment. One of the products of this effort has been the World Digital Magnetic Anomaly Map, the first edition of which was released in 2007. A second, improved, edition is planned for 2011. Interpretations of the lithospheric magnetic field that bear on impacts, tectonics, resource exploration, and lower crustal processes are reviewed. Future interpretations of the lithospheric field will be enhanced through a better understanding of the processes that create, destroy, and alter magnetic minerals, and via routine measurements of the magnetic field gradient. IntroductionThe magnetic field originating in the earth's lithosphere is part of the earth's magnetic field complex, a dynamic system (Friis-Christensen et al. 2009) dominated by the interaction of the earth's magnetic field dynamo with that of the sun's. The lithospheric field M.E. Purucker ( ) Raytheon at Planetary Geodynamics Lab, Goddard Space Flight Center, Code 698, Greenbelt, MD 20771, USA e-mail: michael.e.purucker@nasa.gov is dominated by static (on a human time scale) contributions that typically represents less than 1% of the overall magnitude of the magnetic field complex, and originate from rocks in the crust and locally, the uppermost mantle. Interpretation of the lithospheric magnetic field is used in (1) structural geology and geologic mapping, and extrapolation of surface observations of composition and structure, (2) resource exploration and 3) plate tectonic reconstructions and geodynamics.This article is designed as a review describing recent progress in mapping and interpreting the lithospheric magnetic field, and also includes some highlights from the 2009 IAGA meeting in Sopron, Hungary. Since IAGA meets every four years, we have designed this review to highlight progress in the four year period from 2005 through 2009, although references to earlier important works are not neglected, especially in the area of resource exploration. Several reviews bearing on the mapping and interpretation of the lithospheric magnetic field have appeared between 2005 and 2009. Review articles within books and encyclopedias have included those within the Encyclopedia of Geomagnetism and Paleomagnetism (Gubbins and

Studies on the relationships of the Curie surface with heat flow and crustal structures in Yunnan Province, China, and its adjacent areas

“…Since the 1980s, the application of satellite magnetic survey data to estimate the Curie surface has substantially progressed (Mayhew 1982;Purucker et al 1998;Purucker and Clark 2011). Based on the equivalent magnetic dipole method, Maule et al (2005) used the lithospheric magnetic field model of the CHAMP satellite magnetic surveys (MF3 and MF5) to calculate the depth of the Curie surface for Australia, Antarctica, and Greenland, as well as estimate the density of the terrestrial heat flow.…”

Thermal evolution of the North Atlantic lithosphere: New constraints from magnetic anomaly inversion with a fractal magnetization model

“…Over the last several years, global compilations of magnetic anomalies become available at increasing resolutions (Figure b) [ Hamoudi et al ., ; Hemant et al ., ; Purucker , ; Maus et al ., ]. These valuable data assets, strengthened with improved data processing algorithms, open a new way of investigating large‐scale lithospheric magnetization and geothermal state [e.g., Purucker and Whaler , ; Bouligand et al ., ; Li et al ., ; Li , ; Purucker and Clark , ]. Being a good proxy to subsurface temperature variation, the mapped depth to the Curie‐point temperature puts an observable and direct constraint on the 3‐D geothermal structure of the Atlantic lithosphere, which cannot be easily assessed otherwise.…”

Magnetic Mineralogy and Petrophysical Properties of Ultramafic Rocks: Consequences for Crustal Magnetism

“…This observation indicates the contribution the NRM to in situ magnetization is greater than that of the induced magnetization. However, to interpret the influence of the NRM on the anomaly, it is essential to know the volume and extent of the regions of coherent magnetization (Carporzen et al, 2006;Clark, 2014;Lillis et al, 2010;McEnroe et al, 2018;Purucker & Clark, 2011). The vector average of the Q value (Q v , contrasted with scalar or nominal Q n ) is calculated to take into account variation in NRM directions and intensity (Brown & McEnroe, 2008;Dunlop et al, 2010;McEnroe & Brown, 2000).…”

“…Long-wavelength anomalies originate largely within the lithosphere (Purucker & Whaler, 2015;Purucker & Clark, 2011). Here the thickness of the magnetic crust, the part of the lithosphere above the Curie temperature of ferromagnetic minerals, plays an important role.…”