山东玲珑花岗岩内脉岩年代学特征及地质意义

Chronological Characteristics and Geological Significance of Vein Rocks in Linglong Granite in Shandong Province

在胶东地区广泛分布的中生代侵入岩中发育有玲珑-招风顶、巨山-龙门口和崂山-大珠山三大脉岩带,脉岩成分十分复杂,几乎包括了所有的岩浆岩类型,从超基性基性到中酸性以及碱性脉岩皆有出露,主要有煌斑岩、闪斜云斑岩、辉绿玢岩、辉长岩脉、石英闪长玢岩、闪长玢岩、花岗闪长斑岩、石英二长斑岩、花岗斑岩、二长斑岩、正长斑岩、石英脉和碳酸盐岩脉等,它们应是不同构造期和不同时代的综合产物。该文通过对招远石门郭家-谢家庄一带产于玲珑花岗岩中的三组石英闪长玢岩进行同位素年代学研究,获得LA-ICP-MS锆石U-Pb年龄为119.5±0.9 Ma、118±2.2Ma和116±1.4Ma,代表了石英闪长玢岩的成岩年龄,而在D181199 XT2样品中所获得的176±7.0Ma、156±5.9Ma和118±2.2Ma年龄,后者代表了石英闪长玢岩的成岩年龄,前二个年龄可能是脉岩岩浆在上侵过程中,捕获了先前存在的岩体或玲珑花岗岩的地质信息,是一组继承性或捕获性年龄。同时根据区域内在玲珑花岗岩中获得的中性脉岩年龄数据及其综合分析,认为玲珑花岗岩成岩后至少有二期脉岩侵位,一期发生在142Ma左右,另一期发生在118Ma期间,可能代表了二期地壳浅层次的伸展作用。胶东地区中基性酸性脉岩形成的构造环境、成岩时限与金矿有着内在的成因联系,中基性脉岩中有一期与金矿形成关系密切。

Linglong-Zhaofengding vein rock belt,Jushan-Longmenkou vein rock belt and Laoshan-Dazhushan vein rock belt developed in Mesozoic intrusive rocks which are widely distributed in Jiaodong area.The composition of vein rocks is very complex,including almost all types of magmatic rocks,ultrabasic—intermediate acid and alkaline vein rocks.Main rocks are lamprophyre,hornblende plagioclase mica porphyry,diabase porphyrite,gabbro vein,quartz diorite porphyrite,diorite porphyrite,granodiorite porphyry,quartz monzonite porphyry,granite porphyry,monzonite porphyry,syenite porphyry,quartz vein and carbonate vein,etc.They should be comprehensive products of different tectonic periods and different ages.Through study on isotopic geochronology of three groups of quartz diorite porphyrites in Linglong granite in Guojia-Xiejiazhuang area in Shimen of Zhaoyuan city,the ages of La-ICPMS zircon U-Pb are obtained as 119.5±0.9Ma,118±2.2Ma and 116±1.4Ma respectively.From the D181199 XT2 sample,three ages as 176±7.0Ma,156±5.9Ma and 118±2.2Ma have been obtained.The last age represents the diagenetic age of quartz diorite porphyrite,while the first two ages may be a group of successive or trapping ages,in which geological information of pre-existing rock mass or Linglong granite is captured during the upwelling process of vein magma.At the same time,according to the age data and comprehensive analysis of the neutral dyke obtained from Linglong granite in this area,it is considered that there are at least two stages of dyke emplacement after the formation of Linglong granite,one stage occurs at about 142Ma,the other stage occurs at 118Ma,which may represent the extension of shallow crust in the second stage.The tectonic environment and diagenetic time limit for the formation of intermediate basic CD1 acid dykes in eastern Shandong are closely related to the origin of gold deposits,and one stage of intermediate basic dykes is closely related to the formation of gold deposits.