The Moho as a magnetic boundary revisited

Approximately 400 globally distributed xenolith samples are examined to determine whether continental regions are characterized by relatively magnetic crusts lying on relatively nonmagnetic mantles. Samples of mantle peridotites and mafic granulites by Wasilewski et al. (1979) are supplemented by samples of mantle and crustal xenoliths from Asia, North America, Africa, and Antarctica. The data indicate that a magnetic crustal layer overlies a nonmagnetic mantle much in the same manner as proposed by Jarchow and Thompson (1989). Nonmagnetic chrome spinels and magnesian ilmenites make up the ultramafic upper-mantle xenolith suite. Mafic rocks are the typically magnetic components of the crust, and induced magnetizations can account for long-wavelength magnetic anomalies measured remotely by aircraft and spacecraft.