Paleomagnetism of ca. 1.35 Ga sills in northern North China Craton and implications for paleogeographic reconstruction of the Mesoproterozoic supercontinent

We report paleomagnetic data on precisely dated Mesoproterozoic sills, in zircon and baddeleyite Pb-207/Ph-206 ages of 1345 +/- 12 and 1353 +/- 14 Ma respectively, intruding the Xiamaling and Wumishan formations in North China with an aim of evaluating how the North China Craton (NCC) was involved in the evolution of the Columbia supercontinent from ca. 1.78 to 1.35 Ga. After systematic thermal demagnetization we isolate a high temperature characteristic remanence from 18 sites with a tilt-corrected site-mean direction of D = 294.4 degrees, I= -31.7 degrees and alpha(95) = 4.3 degrees, corresponding to a mean paleomagnetic pole at lambda = 5.9 degrees N, phi = 359.6 degrees E (N= 18) with angular standard deviation of 10.0 degrees and A(95) = 4.3 degrees. Rock magnetic experiments, light microscopy and scanning electron microscopy all indicate that the main magnetic minerals in the sampled sill rocks are medium sized titanomagnetites. The positive fold test and fresh titanomagnetite grains suggest that the characteristic remanence is likely to be a primary acquired at ca. 135 Ga. The preliminary paleogeography reconstruction based upon the well-matched apparent polar wander paths between the Laurentia-Baltica-Siberia united block and the NCC supports the interpretation that the NCC may have drifted together with this united block before ca. 1.35 Ga during the late history of the Columbia supercontinent. We argue that the NCC was located in low latitudes and kept tight connections with the Siberian and Indian cratons during the interval between ca. 1.8 and 1.35 Ga, and that the ca. 1.35 Ga sills widely developed in the Mesoproterozoic Xiamaling and Wumishan formations, as well as the ca. 13-1.2 Ga magma events well-developed in Siberia and northern margin of the NCC, may represent the complete fragmentation of the NCC with the neighboring cratons. (C) 2013 Elsevier B.V. All rights reserved.