USE OF ZIJDERVELD VECTOR DIAGRAMS IN MULTICOMPONENT PALEOMAGNETIC STUDIES

The Zijderveld diagram is a plot of vector magnetization during the course of AF or thermal cleaning, projected on two orthogonal planes. The Zijderveld diagram contains the same information as conventional plots of magnetization direction and intensity, but presents it in a form that permits immediate resolution of superimposed components of magnetization if there exist 'windows' in the coercivity or blocking temperature spectrum in which only one component is demagnetized. In such intervals, the Zijderveld plot has linear segments whose slopes are simply related to the declination and inclination of the resolved component. Although Zijderveld diagrams have been used for more than a decade to define stable primary NRM in the presence of viscous or other noise, they are only beginning to be used to retrieve ancient secondary magnetizations that may be either softer or harder than primary NRM. The Zijderveld method is the most general vector subtraction technique. All possible differences of vectors at different demagnetization steps are represented in a single vector diagram, and it is immediately obvious which subtracted vectors have physical significance. Furthermore, a test for the required non-overlapping coercivity or blocking temperature spectra, namely linearity of a segment or segments of the plot, is built into the Zijderveld technique. Uncertainty in the direction of a resolved component is readily quantified by linear least-squares analysis. Examples of successful 2-component and 3-component Zijderveld studies are drawn from work on viscous submarine gabbros and peridotites of Tertiary age, and metamorphically-overprinted granites, gabbros, metavolcanics and iron formations of early Precambrian age. © 1979.