New Paleomagnetic Results Of Ca.1.68-1.63 Ga Mafic Dyke Swarms In Western Shandong Province,North China Craton: Implications For The Reconstruction Of Columbia Supercontinent

Although Paleo-Meosoproterozoic supercontinent Columbia has been proposed for decades and the position of North China Craton was still skeptical owing to the paucity of available high-quality paleomagnetic and reliable geological constraints.A variety of reconstruction models have suggested that Laurentia,Baltica,Siberia,India and North Australian Craton were candicates which may be adjacent cratons to North China Craton.Precise geochronological dating of extensive Mesoproterozoic mafic dyke swarms in Western Shandong Province?also referring to the Luxi area?,China showed the emplacement ages could be divided into two stages,¹680 Ma and¹630 Ma.Herein we reported new paleomagnetic and rock magnetic results of approximate 160 samples?16 sites?from two stages of mafic dyke swarms in the Luxi area to pinpoint the location of North China Craton within the Columbia supercontinent in this time interval.Rock magnetic experiments confirmed that magnetite was the main magnetic carrier for these dykes and that Fe-sulfides was potential magnetic minerals.In backscattered scanning electron microprobe?SEM?imagery and X-ray mass spectral analysis,experimental results revealed that magnetite of these two stages of dykes was actually titanomagnetite with protogenous high-temperature exsolution lamellae,which indicated titanomagnetite was primary mineral.After stepwise thermal demagnetization,two paleomagnetic poles were obtained.For¹630 Ma dykes,normal and reversed high-temperature remanent magnetization directions were isolated and these directions passed a C-classification reversal test.Considering on protogenous titanomagnetite,field outcrops as well as geological evolution,these high-temperature remanent magnetizations were interpreted as primary remanences which were acquired by dykes during cooling.The corresponding paleomagnetic pole was at 20.8°N,182.5°E(?=28.3,A₉₅=8.3°,N=9).This pole passed the examination of secular variation of geomagnetic field?Deenen,2011,2014?.Moreover,for¹680 Ma dykes,only normal high-temperature remanent magnetization direction was isolated;however,this was also interpreted as primary remanence due to protogenous titanomagnetite of¹680 Ma dykes.The corresponding paleomagnetic pole was at 17.8°N,184.9°E(?=29.6,A₉₅=14.3°,N=5).This pole passed the examination of secular variation of geomagnetic field?Deenen,2011,2014?.Eventually,North China Craton was at mid-low latitudes from¹680 Ma to¹630 Ma,whose paleo-position was consist with other main cratons of the Columbia.The paleomagnetic pole at¹630 Ma fulfilled a Van der Voo?1990?value Q=6.Therefore,this¹630 Ma paleomagnetic pole and¹680 Ma paleomagnetic pole are suggested as a key pole and a reference pole,respectively,for Precambrian continental reconstruction for North China Craton and were selected to depict a more detailed apparent pole wonder path?APWP?for comparison with other main Precambrian cratons.Combining with other coeval paleomagnetic poles of Laurentia,Baltica,Siberia,India and North Australian Craton as well as geological evidences from these cratons,our reconstruction scenario supports the potentially temporal and spatial connection between Baltica,North Australian Craton and North China Craton.It may be possible that the northern margin of North China Craton was linked to northern North Australian Craton while the eastern margin of North China Craton was adjacent or even connected to southern Baltica in Paleo-Mesoproterozoic.