胶东招掖地区滦家河花岗岩锆石U-Pb年代学、岩石地球化学及其地质意义

滦家河花岗岩体是胶东金矿区内的重要岩体,其岩性主要为中粗粒黑云母二长花岗岩。锆石LA—ICP—MS U—Pb年代学研究表明,滦家河花岗岩形成于149±2 Ma,属晚侏罗世。滦家河花岗岩Si O2的含量为64.58%~72.05%,相对较高;A/CNK值为0.98~1.22。微量元素特征显示,滦家河花岗岩富集大离子亲石元素(LILE)Rb、Ba、K,强烈亏损高场强元素(HFSE)Nb、Ta、Ti、P;稀土元素特征显示轻稀土强烈富集,重稀土极度亏损,轻微正铕异常。岩石的Nb/La和Nd/Th比值显示壳源花岗岩的特征,Rb/Sr比值暗示可能有部分幔源物质混入。结合区域地质分析认为,侏罗纪开始,太平洋板块向欧亚大陆的俯冲引发大规模幔源岩浆底侵,导致地壳物质部分熔融形成滦家河花岗岩。

Zircon U-Pb geochronology and petrogeochemistry of Luanjiahe granite in Jiaodong region and their geological significance

Luanjiahe granite is the important rocks in Jiaodong goldfields region， composed mainly of medium- coarse grained biotite monzonitic granites． LA - -ICP - -MS zircon U - -Pb dating shows that the Luanjiahe granite formed in the Late Jurassic (aged in 149 ±2 Ma)． The SiO 2 content of Luanjiahe granite is higher as 64. 58% to 72. 05%，while A/CNK is 0. 98 to 1. 22． The granite is enriched in large ion lithophile elements (LILE) Ｒb、 Ba、K， and strongly depleted in HFSE (Nb、Ta、Ti and P)． The ＲEE patterns demonstrate strong enrichment in LＲEE and depletion in HＲEE，and sightly positive anomaly in Eu． The ratio of the Nb/La and Nd/Th shows char- acteristics of the crust granites． The ratio of Ｒb/Sr shows possible mixture of part of the mantle source materials． Combined with the regional geological analysis，it is suggested that the subduction of the Pacific plate to Eurasian Land triggered massive mantle- derived magma under- plating since Jurassic，led to a partial melting of crust material and the Luanjiahe granite．