Paleomagnetic Constraints From 925 Ma Mafic Dykes in North China and Brazil: Implications for the Paleogeography of Rodinia.

Coeval Neoproterozoic mafic dykes with a well‐constrained isotopic age of 925 Ma are distributed in the North China Craton (NCC) of China and São Francisco Craton (SFC) of Brazil. Several recent studies favor the hypothesis that these two cratons were connected during 925 Ma and constituted building cratons for the supercontinent Rodinia. However, the paleo‐positions of the two cratons in Rodinia have not yet been paleomagnetically resolved. This paper presents the paleomagnetic results of these dykes in both NCC and SFC. Detailed thermal and alternating‐field demagnetization revealed that these dykes record stable components of magnetization with unblocking temperatures below the Curie temperature of magnetite. Rock magnetic results and scanning electron microscope analysis further confirm that the major magnetic minerals in dyke samples are pseudo‐single domain titanomagnetites. The mean directions of the characteristic remanent magnetization (ChRM) of the dykes are distinct from those of rocks of different ages in the sampling localities, and are supported by positive baked contact tests, indicating primary remanent magnetization. The ChRM of the SFC dykes also exhibits dual polarity. Our results suggest that the NCC and SFC were in the moderate to high paleolatitudes of the Southern Hemisphere during approximately 925 Ma, suggesting a possible paleogeographic connection between the two cratons. A new paleogeographic reconstruction of both cratons during 925 Ma is proposed, which is supported by other geological evidence. Plain Language Summary: The formation and breakup of the supercontinent Rodinia have played crucial roles in the global tectonic evolution and paleoclimate changes during the Neoproterozoic which lasted from 1.0 billion to 541 million years ago. The exact configuration of the Rodinia remains debatable, including whether the North China Craton (NCC) and São Francisco Craton (SFC) were integral components of the Rodinia. In this paper, we present new results of an integrated investigation, including paleomagnetic and rock magnetic studies and scanning electron microscope analysis, on the well dated coeval 925 Ma mafic dykes in both NCC and SFC. The results of scanning electron microscope and magnetic measurements confirm the major magnetic minerals and the stability of characteristic remanence directions. The results imply that both NCC and SFC were located at moderate to high paleolatitudes of the Southern Hemisphere during approximately 925 Ma, suggesting the possibility of a paleogeographic connection between the two cratons in the Rodinia. The findings of this study help gain improved understanding of paleogeography of the early Earth. Key Points: Characteristic remanence for the 925 Ma dykes in North China Craton and São Francisco Craton is interpreted as primaryBoth cratons were located at moderate–high paleolatitudes, southwest of Rodinia's core at 925 Ma, suggesting a paleogeographic connectionThe possible paleogeographic connection between the two cratons is supported by new paleomagnetic and geological evidence [ABSTRACT FROM AUTHOR]