Thermal demagnetization furnaces are routine facilities that underpin countless paleomagnetic studies by allowing the progressive removal of naturally acquired magnetic remanence or the imparting of well controlled laboratory magnetization. The ideal thermal demagnetizer should maintain “zero” magnetic field during thermal treatments. However, magnetic field noise, including residual magnetic fields of material used to construct the furnace and induced fields caused by the heating current in the furnace are always present. As technology advances allowing the measurement of ever weaker magnetic remanences, it is essential that high-performance demagnetization furnaces are developed to reduce these sources of magnetic field noise. By combining efficient demagnetization of shielding and a new structure of heating wire, we have developed a new demagnetization furnace with low magnetic field noise. Repeated progressive thermal demagnetization experiments using specimens that were previously completely thermally demagnetized above their Curie temperature were carried out to explore the effects of fields within various types of furnace during demagnetization. These experiments confirm that magnetic field noise in various furnaces can have an observable and detrimental impact on demagnetization behavior and that this is reduced with our new design. The new heating element design and procedure for reducing magnetic field noises represent a significant improvement in the design of thermal demagnetizers and allows for extremely weak specimens to be successfully measured.

Felsic continental crust is unique to the Earth in the solar system, but it still remains controversial regarding its formation, accretion and reworking. The plate tectonics theory has been significantly challenged in explaining the origin of continents as Archean continents rarely preserve hallmarks of plate tectonics. In contrast, growing evidence emerges to support mantle plume-derived oceanic plateau models as the models can reasonably explain the origin of bimodal volcanic assemblages and nearly coeval emplacement of tonalite-trondjhemite-granodiorite (TTG) rocks, presence of ~1600ºC komatiites and dominant dome structures, and lack of ultra-high-pressure rocks, paired metamorphic belts and ophiolites in Archean continents. Although plate tectonics seems to fail in explaining the origin of continents, it has been successfully applied to interpret the accretion or outgrowth of continents along subduction zones where new mafic crust is generated at the base of continental crust through partial melting of the mantle wedge with addition of H2O-dominant fluids from the subducted oceanic slabs, and partial melting of the juvenile mafic crust results in the formation of new felsic continental crust, leading to the outside accretion of continents. Subduction processes also cause the softening, thinning and recycling of continental lithosphere due to the vigorous infiltration of volatile-rich fluids and melts especially along weak layers or weak belts, leading to the widespread reworking and even destruction of continental lithosphere. Reworking of continents also occurs in continental interiors due to plume-lithosphere interactions, which, however, leads to much less degrees of lithospheric modification than subduction-induced craton destruction.

A quick and effective technique is developed to diagnose the geomagnetic dipole field based on an unstrained single circular current loop model. In comparsion with previous studies, this technique is able to separate and solve the loop parameters successively. With this technique, one can search the optimum full loop parameters quickly, including the location of loop center, the loop orientation, the loop radius, and the electric current carried by the loop, which can roughly indicate the locations, sizes, orientations of the interior current sources. The technique tests and applications demonstrate that this technique is effective and applicable. This technique could be applied widely in the fields of geomagnetism, planetary magnetism and palaeomagnetism. The further applications and constrains are discussed and cautioned.