胶东金矿成矿时代及区域地壳演化——基性脉岩的SHRIMP锆石U-Pb年龄及其地质意义

Metallogenic epoch and regional crust evolution in the Jiaodong gold deposit,Shandong Province: Evidence from SHRIMP zircon U-Pb ages of mafic dykes

关于胶东金矿的成矿时代前人已进行了较多研究,但其成矿时限尚没有准确确定。对胶东焦家金矿床成矿前和成矿后的2个基性脉岩进行了锆石SHRIMP年龄测定和锆石氧同位素分析。锆石阴极发光图像显示,样品中有少量岩浆新生锆石,其晶形、环带清晰。在2个成矿前脉岩样品中测得岩浆锆石206Pb/238U年龄最小值为124.9±1.8Ma和124.2±1.1Ma,1个成矿后脉岩样品中测得最小年龄值为112.2±0.7Ma。故成矿前脉岩的侵位年龄小于等于124.9Ma和小于等于124.2Ma,成矿后脉岩的侵位年龄小于等于112.2Ma,金矿的成矿年龄被限制在124~112Ma之间。此外,较多的锆石年龄数据记录了早侏罗世、三叠纪、古生代、新元古代、中元古代和新太古代的岩浆事件和变质事件,指示胶北隆起深部既有华北克拉通新太古代、中元古代和新元古代的地质体或地质事件,也有苏鲁造山带古生代和三叠纪的地质体或地质事件,苏鲁超高压变质带曾俯冲到胶北隆起之下。锆石氧同位素组成变化范围较大,δ18O值为3.86‰~11.37‰,指示了不同时代锆石氧同位素组成的不均一性和物质来源的差异性。

Although mineralogenetic epoch of the Jiaodong gold deposit in Shandong Province has been studied by many previous researchers, the accurate time frame of mineralization remains undecided. This paper reports SHRIMP zircon ages and oxygen isotopic values for pre-metallogenic and post-metallogenic mafic dykes in the Jiaojia gold deposit of Jiaodong Peninsula. In CL photos,the igneous zircons show good crystal form and clear zoning. Two samples from pre-metallogenic mafic dykes have recorded concordant ages of 124.9±1.8 Ma（n=2,MSWD=2.2）and 124.2±1.1 Ma（n=2, MSWD=0.50）. A sample from post-mineraliza-tion lamprophyre yielded a concordant age of 112.2±0.7 Ma（n=1）, and therefore the emplacement age of the pre-metallogenetic mafic dykes is ≤124.9 Ma and ≤124.2 Ma. The emplacement age of the post-mineralization lamprophyre is ≤112.2 Ma. The metallogenic age of the Jiaojia gold deposit is ≤124.2 Ma. These data indicate that time limitation of mineralization of the Jiaojia gold deposit should be from 124 Ma to 112 Ma. Besides, the obtained multiple stages of inherited zircon ages from the samples have recorded the magmatic and/or metamorphic events of Jurassic, Triassic, Paleozoic, Neoproterozoic, Mesoproterozoic and Neoarchean.This suggests that, in addition to Neoarchean, Mesoproterozoic and Neoproterozoic geological bodies in North China Craton,there are also Paleozoic and Triassic geological bodies from Sulu orogenic belt in the depth of the Jiaobei uplift. These data suggest that the materials of the Sulu ultrahigh-pressure metamorphic belt was thrusting under the Jiaobei uplift. The δ18 O values of zircons vary from 3.86‰ to 11.37‰, and this indicates that different stages of zircons have diverse oxygen isotope compositions and diversified material sources.