TESTING THE TWINS HYPOTHESIS: WERE GREATER NORTH CHINA AND WESTERN LAURENTIA LINKED IN THE ARCHEAN AND PROTEROZOIC?

The North China craton figures importantly in the tectonic development of Asia but the evolution of its past geometry through the Phanerozoic has never been systematically investigated. As a result, the position and connection of this ancient craton in the Archean and Proterozoic global reconstructions is still uncertain. Restoration of the original shape of Greater North China, which includes the North China, Tarim, and Karakum cratons from east to west, requires removing Phanerozoic intra-continental deformation, continental distortion, marginal rifting, and continental subduction. Our restoration suggests that the Greater North China has an along-strike east-west length of > 6000 km. This cratonal strip has no pre-Neoproterozoic passive margin deposits on its boundaries and numerous Proterozoic orogens are inexplicably truncated, which requires Greater North China to fit into a larger continental assembly prior to the early Neoprotoerozoic. As part of the recently proposed TWINS hypothesis, Greater North China may have been affixed to the western edge of Laurentia. A key test to this hypothesis is to examine the Archean and Proterozoic basement of the cratons. We have carefully examined the existing literature—augmenting this information with our own observations, especially in North China—to asses the feasibility of a linkage between Greater North China and western Laurentia. We specifically note correlations between: (1) the >2.5 Ga Eastern Block of North China, Grouse Creek block, and Wyoming Province; (2) the Western Block of North China, with up to 3.4 Ga gneiss intruded by 2.6 Ga plutons, the 1.8 – 2.7 Ga Priest River complex, and the Medicine Hat block, with up to 3.3 Ga gneiss intruded by 2.6 – 2.7 Ga plutons; and (3) the 1.8 – 1.9 Ga Trans-China orogen and Great Falls tectonic zone that joins these older cratonal units, both of which may have involved southward subduction (in Laurentian coordinates) prior to collision. Both regions have similar rifting histories and may have separated in the Neoproterozoic. This resulted in the formation of the Paleo-Asian and Pacific Oceans (two "twins"), which were not separated until the closure of Greater North China around Siberia and the Central Asian Orogenic System in the Permian.