OurfieldworkandgeochronologicstudiesinnorthernHebeiandwesternLiaoningareasindicatethatthemajorMesozoiccontractionaleventsintheYanshanbeltareof(1)pre-MiddleJurassic(Indosinian?),(2)LateJurassicand(3)EarlyCretaceousage.ThefirstN-SshorteningcouldbeaconsequenceofthecollisionoftheMongolianarcsalongtheSolonsutureagainsttheNorthChinaplate.Siberian-NorthChinaplatecolli-
