New paleomagnetic results from the ca. 1.68-1.63 Ga mafic dyke swarms in Western Shandong Province, Eastern China: Implications for the reconstruction of the Columbia supercontinent

摘要

The existence of Paleo-Mesoproterozoic supercontinent Columbia (aka Nuna) was established decades ago, but the position of North China Craton within Columbia is still highly debated due to the paucity of available high-quality paleomagnetic and reliable geological constraints. Precise geochronological dating of extensive Mesoproterozoic mafic dyke swarms in Western Shandong Province (also named the Luxi area), China reveals two phases of dyke emplacement at similar to 1.68 Ga and similar to 1.63 Ga. In this paper, we report new paleomagnetic and rock magnetic results obtained from approximate 160 samples (16 sites) collected from these two phases of mafic dyke swarms in the Luxi area with the aim of pinpointing the location of North China Craton within Columbia supercontinent in this time interval. Rock magnetic experiments confirm that either magnetite or titanomagnetite is the main magnetic carrier in these dykes. Stepwise thermal demagnetization revealed two paleomagnetic poles. For the similar to 1.63 Ga dykes, normal and reversed high-temperature remanent magnetization directions yield a mean direction (D/I) of 86.1 degrees/53.5 degrees (kappa = 43.3, alpha(95) = 7.9 degrees, N = 9). These directions pass a reversal test and are interpreted as primary remanences. The corresponding paleomagnetic pole is calculated at 20.8 degrees N, 182.5 degrees E (kappa = 28.3, A(95) = 8.3 degrees, N = 9). This pole passes the examination of secular variation of geomagnetic field (Deenen et al., 2011, Deenen et al., 2014). It fulfills a Van der Voo (1990) value Q = 6 and is therefore suggested to be a key pole demarcating the Precambrian North China Craton. For the similar to 1.68 Ga dykes, only the normal directions are isolated with a mean direction (D/I) of 89.1 degrees/47.1 degrees (kappa = 35.0, alpha(95) = 13.1 degrees, N = 5) with a corresponding paleomagnetic pole of 17.8 degrees N, 184.9 degrees E (kappa = 29.6, A(95) = 14.3 degrees, N = 5). This pole passes the examination of secular variation of geomagnetic field. Finally we select the similar to 1.63 Ga high-quantity paleomagnetic pole in order to depict a more detailed apparent pole wander path (APWP) to compare with the other major Precambrian cratons. Combined with other geological evidence, our reconstruction scenario supports the spatio-temporal connection between the Baltica, North Australian Craton and North China Craton.