Solonker Suture in East Asia and its bearing on the final closure of the eastern segment of the Palaeo-Asian Ocean

Abstract

The location and tectonic nature of the Solonker Suture in East Asia and hence the late Palaeozoic to early Mesozoic closure of the Palaeo-Asian Ocean have notoriously been enigmatic in the past decades due to limited rock exposure and the absence of unambiguous collision-related regional features. Several tectonic models have been proposed since, but in many cases these models were derived only from single key exposures or methodologies, often being over-simplified, or -interpreted, leading to questionable extrapolations on regional and global scales despite the complexity of the Palaeozoic accretionary tectonic framework. Now, the regionally consistent availability of geochronological, geochemical, stratigraphic and palaeo-geographic data enables us to integrate these into a highly detailed and coherent Palaeozoic tectonic review of the suture.

The region across the Solonker Suture can generally be subdivided into three major Palaeozoic tectonic provinces, e.g., (i) a Sino-Cratonic Province that resembles the active Palaeozoic northern margin of the North China Craton to the south of the suture, (ii) a Mongolian Province that comprises the south-eastern margin of the Mongolian Terrane to the north of the suture, and (iii) an East Asian Pre-Pacific Province in north-east China that accreted with the Late Permian initiation of Pacific Plate subduction. The Sino-Cratonic Province experienced episodic tectonic activity that includes the accretion of the initially ensialic Bainaimiao Arc onto the passive northern margin of the North China Craton at ~ 437–453 Ma, subsequent southward directed subduction activity beneath the amalgamated margin until at least ~ 400 Ma, followed by a temporary cessation of magmatic activity accompanied by a switch from north- to southward directed continental drift, and finally concluded by renewed subduction activity until the final closure of the Palaeo-Asian Ocean. The Mongolian Province is suggested to have been more closely associated with the Siberian Craton before the presumably Late Devonian opening of the Mongol-Okhotsk Ocean. The East Asian Pre-Pacific Province, originally rifted away from the eastern margin of Gondwana at ~ 600–750 Ma, recorded early Palaeozoic (~ 500 Ma) orogenic processes along the then northern margin of the Siberian Craton. The Baolidao arc system successively developed along the present-day south-eastern margin of the Mongolian Province due to continued subduction activity throughout the Palaeozoic. After the Middle Carboniferous opening of the Hegenshan back-arc basin renewed subduction beneath a matured Baolidao Arc during Carboniferous and Permian times led to the obduction of the Hegenshan ophiolite not earlier than ~ 270 Ma. Shortly after the Palaeo-Asian Ocean diachronously closed from west to east along the Solonker Suture in the Late Permian to Early Triassic. The East Asian Pre-Pacific Province re-attached itself by the mid-Mesozoic, followed by a change in the regional stress regime controlled by Palaeo-Pacific plate subduction.

A divergent double-sided subduction model for the closure of the Palaeo-Asian Ocean provides, based on the reviewed data, a tectonic model that is not only able to reasonably well explain the absence of typical collision-related features in the region but also the abundance of Mesozoic A-type granitic magmatism in north-east China.