辽西早白垩世义县组火山岩的起源及壳幔相互作用

THE ORIGIN OF EARLY CRETACEOUS VOLCANIC ROCKS OF YIXIAN FORMATION AND CRUST -MANTLE INTERACTION IN WEST LIAONING PROVINCE,EASTERN CHINA

对燕山造山带辽西早白垩世义县组火山岩的 Nd,Sr,Pb同位素分析 ,作者认为义县组火山岩起源于岩石圈地幔的部分熔融 ,岩浆在上侵过程中发生了结晶分异和同化混染作用 ,即 AFC过程。与新生代汉诺坝玄武岩中的中生代镁铁质麻粒岩捕虏体和太古代片麻岩对比研究 ,发现义县组火山岩与这些镁铁质麻粒岩捕虏体有许多地球化学相似之处 ,而与长英质麻粒岩捕虏体和太古代各种片麻岩差别较大。作者认为早白垩世燕山板内造山带发生了强烈的岩石圈伸展作用 ,辽西义县组火山岩和汉诺坝新生代玄武岩中的镁铁质麻粒岩捕虏体均为这一构造背景下的产物 ,它们属于幔源岩浆喷发与大规模玄武zh质岩浆底侵作用形成的“同质异相体”

Based on the study of Nd,Sr and Pb isotopes for volcanic rocks of early Cretaceous Yixian Formation in West Liaoning Province and in contrast with granulite xenolithes in Hannuoba Cenozoic basalts and gneiss of Archean,the authors find that the geochemic features of volcanic rocks of Yixian Formation are similar to those of the Mesozoic mafic-granulite xenolithes in Hannuoba Cenozoic basalts instead of the felsic granulite xenolithes in Hannuoba Cenozoic basalts and gneiss of Archaean.It is considered that the basalts of Yixian formation were derived from partial melting of lithosphere mantle and suffered the fractional crystallization and crustal contamination during magma rising. Large scale lithosphere extension and underplating of basaltic magma occurred in intracontinent orogenic zone of Yanshan from late Jurassic to early Cretaceous. Mafic granulite xenolithes in Hannuoba Cenozoic basalts and basalts of Yinxian Formation were formed in this event, and might be the equivalent of the intrusion and eruption of basaltic magma.