华北克拉通东缘金岭杂岩体岩浆源区及构造背景:来自岩相学、岩石地球化学及年代学的证据

Magma source and tectonic setting of Jinling pluton in eastern North China Craton:Evidences from petrography,petrogeochemistry and chronology

金岭杂岩体由细粒黑云角闪闪长岩、中细粒黑云角闪闪长岩、中细粒黑云角闪二长闪长岩和细粒角闪二长闪长岩组成,是鲁西地区典型矽卡岩型富铁矿(金岭铁矿)控矿岩体。本次研究对细粒黑云角闪闪长岩和细粒角闪二长闪长岩进行了锆石LA‐ICP‐MS U‐Pb定年,其结果分别为129.2±3.2 Ma和132.8±1.2 Ma,表明该杂岩体的侵位时代为早白垩世。样品SiO2、K2O和Na2O含量分别介于54.17%~63.73%、1.92%~4.76%和3.10%~5.41%之间,K2O/Na2O为0.58~0.94,A/CNK为0.60~0.93,具有轻稀土富集,重稀土亏损的右倾型稀土配分模式,轻、重稀土分馏程度中等((La/Yb)N=9.94~23.49),Eu异常不明显(δEu=0.84~1.10),具中—弱负Ce异常(δCe=0.56~0.92)。样品以富集大离子亲石元素(Ba、K、U、Pb等)、亏损高场强元素(Nb、Ta、Ti)以及高Sr/Y为特征。金岭杂岩体为燕山晚期岩浆活动产物,属准铝质高钾钙碱性系列,岩浆主要来源于富集岩石圈地幔的部分熔融,并在岩浆上升侵位的过程中有地壳物质的同化混染。燕山晚期华北克拉通在古太平洋板块俯冲后后撤引起的板内伸展环境下,增厚陆壳减薄阶段,岩浆上侵就位形成金岭杂岩体。

Jinling pluton,which is genetically related to giant Jinling skarn iron deposit,mainly composed of fine grained biotite amphibole diorite,medium‐fine grained biotite amphibole diorite,medium‐fine grained biotite amphibole monzodiorite,fine grained amphibole monzodiorite.This study presents zircon LA‐ICP‐Ms U‐Pb ages for fine grained biotite amphibole diorite and fine grained amphibole monzodiorite.The zircon of the two studied rocks yield mean ages of 129.2±3.2 Ma and 132.8±1.2 Ma,respectively,indicating that they emplaced in Early Cretaceous.All diorites have very similar geochemical characteristics.Their SiO2,K2O,Na2O,K2O/Na2O and A/CNK range from 54.17%~63.73%,1.92%~4.76%,3.10%~5.41%,0.58~0.94,0.60~0.93 respectively.It's enriched in LREE and depleted in HREE,distribution curve are right‐leaning,LREE and HREE fractionation is medium((La/Yb)N=9.94~23.49).Normalized REE pattern show a rightward inclination with no Eu anomalies(δEu=0.84~1.10)and medium to weak negative Ce anomalies(δCe=0.56~0.92).Trace elements are characterized by enrichment of LILEs(such as Ba,K,U,Pb),depletion of HFSEs(such as Nb,Ta,Ti)and high Sr/Y.This study demonstrates that Jinling pluton belongs to metaluminous high K calc‐alkaline series and they were the product of Late Yanshanian magmatic activity.Jinling pluton was derived from metasomatized lithosphere mantle and contaminated by some amount of crustal materials during the magmatic processes.We suggest Jinling pluton formed in response to Yanshanian significant NCC thinning,which might be caused by paleo‐Pacific slab subduction.