Mesoproterozoic accretionary orogenesis: Evidence from-1.4 Ga metamorphism on the southeastern margin of the North China Craton

The Mesoproterozoic period has always been thought of as an orogenic quiescence stage. However, contemporaneous magmatism and metamorphism indicate that this period was relatively restless. A Mesoproterozoic metamorphic event (-1.4 Ga) was first discovered in the southeastern part of the North China Craton. Samples, including garnet amphibolite and its countryrock biotite plagiogneiss, were collected from Rushan city on the Jiaodong Peninsula. The major elements of the rock are characterized by high Ti, where the trace elements show slight depletions in Th, U and Sr contents, and the REEs show E-MORB like patterns. The mineral assemblage of the garnet amphibolite includes garnet, hornblende and plagioclase. These metamorphic minerals are also found in zircons as inclusions. Cloudy and homogeneous CL images and flat HREE patterns of zircon trace elements in garnet amphibolite indicate a metamorphic origin, and zircon U-Pb age dating obtained an - 1.4 Ga metamorphic age, which is consistent with the second age group age of the countryrock. Our dating results suggest that the Meoproterozoic metamorphic event in the North China Craton is comparable to metamorphic events reported in the Laurentian and Australian Cratons. Similar magmatism and comparable stratigraphy of these ancient cratons also support the Mesoproterozoic era was not an orogenic quiescence stage. Therefore, we infer a giant orogenic belt that existed along the outer margin of the supercontinent of the Columbia in the Earth's middle age. Long-lived Mesoproterozoic accretionary orogenesis probably affected the edges of supercontinents in a transition stage from the breakup of Columbia to the assembly of Rodinia.