Where and when did the Paleo-Asian ocean form?

Abstract

The closure of the long-lived Paleo-Asian Ocean generated the Central Asian Orogenic Belt (CAOB). However, the tectonic history and circumstances of where and when this ocean formed are poorly constrained. We provide a new perspective to help resolve this problem. Three typical magmatic events marked by a 1.75 Ga charnockite, 1.64 Ga gabbro and 1.35 Ga dolerite dykes in SW Siberia are identical with 1.75 Ga anorthosite, 1.63 Ga basalt and 1.35 Ga dolerite sills in the northern North China craton. The youngest coeval dykes/sills (1.35 Ga) and ∼1.35 to 1.25 Ga sedimentary passive margins in both craton margins mark the initial stage of rifting, and therefore the birth of the Paleo-Asian Ocean. Paleomagnetic data indicate that Siberia and North China drifted together and rotated at similar degrees from ～1.6 Ga to ∼1.35 Ga, suggesting the two cratons were close. After 1.35 Ga, North China rotated in an opposite direction away from Siberia, suggesting further expansion of the Paleo-Asian Ocean, which is consistent with the geological record of the CAOB. The separation between Siberia and North China at the 1.35 Ga was a relatively local event with respect to the Nuna supercontinent, and it did not have significant impact on global tectonics and ocean chemistry. The ocean between Siberia and North China opened and closed from 1.35 Ga to 250 Ma, and thus took ∼1.1 Ga to complete, indicating that the Wilson Cycle operates at different time-scales ranging from 100 Ma in a short collisional orogen to 1.1 Ga in a long-lived accretionary orogen.