Paleomagnetism of the Neoproterozoic Blekinge-Dalarna Dolerites in Western Sweden and Implications of the Sveconorwegian Loop(s)

Laurentia and Baltica are regarded to be juxtaposed at the core of the supercontinent Rodinia during Early Neoproterozoic. This contention is supported by the similar apparent polar wander paths (APWPs) of Laurentia and Baltica, known as the Grenville and the Sveconorwegian loops, respectively. Despite the debates of the age and shape of the Grenville loop, the Sveconorwegian loop has uncertainties as well. Paleomagnetic studies from Baltica show two distinct remanence directions at ca. 950 Ma: one is steep and upwards (A-type) and another is shallow and bipolar (B-type). The fidelity of B-type remanence is supported by the new key-pole from the 935 ± 5 Ma Blekinge-Dalarna dolerites (BDD) in western Sweden. But A-type remanence, less common, is also observed in the BDD dykes. Some studies attribute A-type remanence to remagnetization without clear evidence. If A-type remanence is primary, this would suggest a large APWP excursion of Baltica within a very short duration, analogous to the mid-Ediacaran situation of Laurentia that has been explained by different hypotheses such as true polar wander, unusual geomagnetic configuration or rapid plate motions. Therefore, we conducted a more detailed paleomagnetic study of the BDD dykes that cover an area of 10,000 km2. We propose a combined geochemical and magnetic fabric study to compare BDD dykes' signatures with published results to aid field identification. Thermal demagnetization is conducted and the fidelity of the remanence is examined by rigorous baked contact tests in different host rocks. Dykes with primary remanence will be radiometrically dated to constrain the age of the remanence. This study should have wide implications, in particular the configuration of Sveconorwegian loop(s) in Early Neoproterozoic time, the paleogeographic connection between Laurentia and Baltica in Rodinia, as well as the geodynamics in Earth's deep interior.