吉林老虎山火山区中新世碱玄岩成因及其构造意义

Genesis and Tectonic Significance of Miocene Tephrite in Laohushan Volcanic Area,Jilin Province

老虎山单成因火山位于吉林省大口钦地区.为了探讨火山区中新世碱玄岩的地球化学特征、成因及其与区域断裂构造演化的耦合性,对其开展了全岩地球化学和Pb同位素研究.碱玄岩中Na_(2)O/K_(2)O=1.30~1.38,A/CNK值(0.97~1.09)偏低,Mg^(#)值(58.05~61.11)偏高,富集Th、U、Nb等高场强元素(HFSEs),相对弱富集Rb、Ba、K等大离子亲石元素(LILEs),LREE/HREE=10.66~11.32,^(206)Pb/^(204)Pb、^(207)Pb/^(204)Pb和^(208)Pb/^(204)Pb值范围分别为17.661~17.675、15.451~15.457和37.652~37.692.成岩岩浆主要来源于软流圈地幔,混有少量俯冲洋壳物质,显示出OIB或板内交代富集型地幔源的属性,岩浆形成深度范围约在93~105 km,伊通-舒兰断裂的存在为火山深部岩浆的上升与裂隙式喷发提供了通道和空间,玄武质岩浆的形成及其对应的火山活动发生于伸展构造环境中.

The Laohushan monogenic volcano is located in Dakouqin area,southern Jilin Province.In order to explore the geochemistry characteristics and genesis of the Miocene tephrite in this volcanic area,together with the coupling between it and the evolution of regional fault structure,the whole rock geochemistry and Pb isotope study on it were carried out.Na_(2)O/K_(2)O values of the tephrites are range from 1.30 to 1.38,with low A/CNK(0.97-1.09)and high Mg^(#)(58.05-61.11)values.The tephrites are enriched in high field strength elements(HFSEs),such as Th,U and Nb,and relatively weakly enriched in large ion lithophile elements(LILEs),such as Rb,Ba and K,with LREE/HREE=10.66-11.32.The values of ^(206)Pb/^(204)Pb,^(207)Pb/^(204)Pb and ^(208)Pb/^(204)Pb are range from 17.661 to 17.675,15.451 to 15.457 and 37.652 to 37.692,respectively.The parental magma is mainly from the asthenosphere mantle,with a small amount of subducted oceanic crust components,which shows the attribute characteristics of OIB(oceanic island basalt)or intraplate metasomatic enriched mantle source.The depth range of magma formation is about 93-105 km,and the existence of the Yitong-Shulan fault provides conduit and space for magma upwelling and fissure eruption.In addition,the formation of basaltic magma and its associated volcanic activity occurred in an extensional tectonic environment.