Paleomagnetism, paleointensity and geochronology of a Proterozoic dolerite dyke from southern West Greenland

Abstract

Archean to Paleoproterozoic rocks potentially record the evolution of the geodynamo and the tectonic mode of the early Earth. The paleomagnetic intensity and direction data provide important information on the Earth’s core–mantle revolution. Herein, we report the results of paleomagnetic and geochronological studies of a Proterozoic dolerite dyke from southern West Greenland. Clinopyroxene grains from the dyke yielded Ar–Ar plateau ages from 1808 to 1887 Ma (1816.0 ± 14.6 Ma; 2σ). The paleomagnetic direction of the dyke (D = 243.6°, I = 66.3°, α95 = 3.9°) yielded a virtual geomagnetic pole (VGP) of 33.5 °N and 96.4 °W. This 1.8 Ga pole falls in a limited area where Paleoproterozoic poles between 2.5 Ga and 1.7 Ga for southern West Greenland are distributed. Comparison of the Paleoproterozoic poles of southern West Greenland with those of North America suggests that the North Atlantic Craton of southern Greenland could have been an independent stagnant tectonic block, different from the drifting Superior and Slave Cratons in the Early Proterozoic. Thellier experiments on 13 specimens yielded a mean paleointensity value of 14.8 ± 2.3 μT, indicating a virtual dipole moment of 2.88 ± 0.46 × 1022 Am2. This value is approximately one-third of the present-day Earth's field intensity, and is consistent with the value for the period between 1400 Ma and 2400 Ma. This small paleointensity value of the Proterozoic rocks is due to a gradual dipole moment change over a long period (∼1 Gyrs) since 4000 Ma.