Notes to Paleomagnetism Basics: Reversal History
Reversals and secular variation recorded by the lava flows in Iceland
The left figure shows a sequence of basalt lava flows exposed along a gully at Storutjarnir, north central Iceland. This section covers about 500 m in height and comprises 90 lava flows. K-Ar ages ranging from 2 to 3 Ma were reported for some of the lava flows.
Paleomagnetic study of this section revealed detailed history of secular variation and reversals of the paleomagnetic field as shown in the right figure. In the figure, a small red circle is the VGP position and a larger circle around it is its 95% confidence. Three normal and three reversed polarity periods are included in the section and equal area plots of VGPs were drawn for each polarity period successively from the base to the top. Considering the K-Ar ages of 2-3 Ma and comparing to GPTS, it was concluded that most part of this section was formed in Chron C2An (Gauss) and the lowest part in Chron C2Ar (Gilbert). From this section, statistical features of the paleodirections together with the strength of the paleomagnetic field (paleointensity) were studied in detail.
Following pages will summarize some of the basics of paleomagnetic method.
Reference:
- Tanaka, H., and Y. Yamamoto, Palaeointensities from Pliocene lava sequences in Iceland: emphasis on the problem of Arai plot with two linear segments, Geophys. J. Int., 205, 694-714, 2016. (→ doi:10.1093/gji/ggw031)