2 . early jurassic mafic volcanic rocks in yanshan area were derived from decompression melting of an ancient continental lithospheric mantle , which had been previously metasomatized by subducted slabs during the closure of paleo - asian ocean ; the mantle source of late jurassic mafic volcanic rocks were contributed by dominant emi and insignificant subducted metasomatic components ; early cretaceous mafic volcanic rocks were derived from decompression melting of an ancient continental lithospheric mantle ( emi ) . with regard to the basaltic lavas , the felsic rocks resulted from partial melting of continental crust , which closely related to basaltic underplating 2燕山地区早侏罗世中基性火山岩来自于早期俯冲交代的古老岩石圈地幔部分熔融作用，俯冲交代作用可能与早期古亚洲洋闭合事件有关；晚侏罗世中基性火山岩更多来自于类似于emi型地幔源区的部分熔融作用，俯冲交代成分贡献很弱；早白垩世基性火山岩则来自于emi型地幔源区的部分熔融作用。
