New geochronologic and paleomagnetic results from early Neoproterozoic mafic sills and late Mesoproterozoic to early Neoproterozoic successions in the eastern North China Craton, and implications for the reconstruction of Rodinia.

The interval from the late Mesoproterozoic to early Neoproterozoic is generally considered as a critical time for the amalgamation of Rodinia. The location of the North China Craton (NCC) in Rodinia remains contentious and demands greater paleomagnetic constraints. A combined geochronologic and paleomagnetic study was conducted on the late Mesoproterozoic to early Neoproterozoic rocks in the eastern NCC. Three sills were dated at ca. 945 Ma and one at ca. 920 Ma through use of the zircon U-Pb secondary ion mass spectroscopy method. Paleomagnetic investigation revealed no significant discrepancy between these sills. A positive baked-contact test, secular variation test and presence of reversals together support the primary origin interpretation for the remnant magnetization. A high-quality pole at (28.2 °S, 141.9 °E, A95 = 10.4°) was thus obtained by averaging our new results and a virtual geomagnetic pole previously reported for a ca. 920 Ma sill in the region. These Neoproterozoic sills intruded the successions that contain correlative strata that are named Nanfen, Xinxing, and Liulaobei formations in Liaoning, Jiangsu, and Anhui provinces, respectively. The Nanfen Formation and its equivalents are constrained between ca. 1120 and ca. 945 Ma by detrital zircons and the well-dated mafic sills. The paleomagnetic inclinations observed from the lower parts of the Nanfen, Xinxing, and Liulaobei formations are notably steep. The corresponding poles from these rock units are consistent and averaged at 38.6 °N, 136.7 °E (A95 = 3.2°). The quality of this pole is strengthened by a positive reversal test and its distinctiveness from the younger poles of the NCC. In the middle part of the Nanfen Formation, however, the paleomagnetic directions are characterized by moderate inclinations, being significantly different from those in the lower part of the Nanfen Formation and its equivalents. The calculated pole for the upper part of the Lower Member of the Nanfen Formation is at 8.0 °N, 128.5 °E (A95 = 7.9°). Another pole obtained from the Middle Member of the Nanfen Formation is at 11.2 °S, 127.7 °E (A95 = 8.5°). These two poles also differ from the younger poles of the NCC and likely represent the primary remanences. Our new results, together with the existing global paleomagnetic data and geological evidence, aided by the "right-way-up" connection model between Laurentia and Baltica in Rodinia, support a NCC--NW Laurentia connection between ca. 1120 and 890 Ma. [ABSTRACT FROM AUTHOR]