Paleointensity determination on a 1.786 Ga old gabbro from Hoting, Central Sweden

Paleointensities from Precambrian rocks are rare and might be biased by remagnetization processes. Here we present new analyses of samples from a 1.786 Ga gabbro near Hoting, Central Sweden. Rock magnetic and mineralogical analyses indicate that one of the sites (site 5) may be pristine, whereas the others exhibit evidence of alteration.Characteristic remanent magnetization was determined using principal component analysis for each sample and was compared with results obtained in a previous study of Elming et al. (2009). Intensity measurements from site 5 show higher values compared to those of the other sites, suggesting that alteration processes may lead to underestimation of the field intensity.After cooling rate and anisotropy correction, the field moment at 1.786 Ga was estimated to be 25.6 ± 3.3 ZAm2 and 15.2 ± 6.1 ZAm2 from site 5 only and from all sites respectively. We consider the result from site 5 to be more accurate owing to the lack of evidence for alteration; our estimates agree well with the Proterozoic VDM values suggested by Biggin et al. (2009).

► Measured paleointensity of a 1.786 Ga old Gabbro from Sweden.
► Magnetic mineralogy and its alteration analysed with rock magnetics and microscopy.
► Pristine samples yield higher paleointensities than altered ones.
► One of seven sites is pristine and yields the most reliable results.
► These high quality measurements indicate a low intensity during Precambrian.