苏鲁造山带东段小珠山高分异花岗岩地球化学特征与成因探讨  

Geochemical characteristics and genesis of Xiaozhushan highly fractionated granite in the eastern segment of Sulu Orogenic Belt

作　　者：刘瑞杨 LIU Ruiyang(State Key Laboratory of Continental Dynamics,Northwest University,Xi’an 710069,China)

机构地区：[1]西北大学大陆动力学国家重点实验室,西安710069

出　　处：《华北地质》2025年第1期24-43,共20页North China Geology

基　　金：山东省重大科技创新工程项目“山东东部海域日青威盆地油气赋存条件研究(2017CXGC1608)”;中石化科技部项目“北黄海—渤海湾盆地低勘探程度区勘探潜力评价(P20028)”;中石化石勘院开放基金“深水混合沉积过程及其对页岩储层发育的控制作用——以日青威盆地莱阳组为例(HX20220005)”;国家自然科学基金项目“前寒武地层中记录的地球规道参数研究(41772190)”。

摘　　要：【研究目的】小珠山位于山东东部苏鲁造山带东延部分,该地区广泛出露中生代花岗岩。笔者在野外踏勘过程中发现了淡色、矿物颗粒大的花岗岩剖面,后经地球化学测试确定为高分异花岗岩。高分异花岗岩是大陆地壳成分成熟度的重要标志,故本研究旨在完善研究区花岗岩种类及其含矿性潜力评价。【研究方法】对在小珠山地区取得的8件样品进行岩相学、全岩主微量及稀土元素、Sr-Nd-Pb同位素、锆石U-Pb测年与原位Hf同位素、X射线衍射和激光拉曼光谱、斜长石电子探针、元素面扫原位分析。【研究结果】得到以下结论:岩相学表明研究区花岗岩含有S型花岗岩特征矿物-堇青石,存在明显伟晶岩脉。伟晶岩是花岗质岩浆结晶分异的产物,预示着小珠山S型花岗岩具有成矿潜力。10000 Ga/Al-Zr图解表明研究区花岗岩为I和S型两种,样品为高硅花岗岩(SiO_(2)>71.9%),全碱含量高(Na_(2)O+K_(2)O>8.5%),属于过铝质高钾钙碱性系列。计算高分异花岗岩的常见指数:多数样品Eu负异常明显(δEu=0.4~0.5),铝饱和指数较高(A/CNK>1.2),分异指数(DI)在90以上。锆饱和温度反映岩浆起源温度为832~875℃,锆石Ti温度计反映岩浆结晶温度为618.8~726.44℃,说明岩浆分异经历明显降温过程。Sr-Nd-Pb同位素显示高I_(Sr)(0.6999~0.7210)和低ε_(Nd)(t)(﹣18.7~﹣12.4),(^(206)Pb/^(204)Pb)i=16.3140~16.6760,(^(207)Pb/^(204)Pb)i=15.4450~15.4645,(^(208)Pb/^(204)Pb)i=36.8110~37.2909,表明样品岩浆源区为壳源。年代学表明样品年龄为116.4 Ma,为早白垩世高分异花岗岩。【结论】上述结论说明研究区高分异花岗岩是以壳源物质为主的岩体。分异过程经历斜长石以及锆石、磷灰石等副矿物的分离结晶,岩浆沿岛弧裂缝上涌,形成了具有含矿潜力(DI=83~95)的高分异花岗岩。[Objective]Xiaozhushan is located in the eastern extension of the northern Jiaonan Uplift,Sulu orogenic belt,Shandong Province,adjoining the Wulian-Qingdao fault.Mesozoic granites are widely exposed in this area.In the process of field exploration,the lightcolored granite profile with large mineral particles were founded,which determined as highly differentiated granite by geochemical tests.Highly fractionated granite is an important symbol of continental crust composition maturity.This study plays an important leading role in improving the types of granites in the study area,evaluating the ore-bearing potential of the study area,and exploring the large igneous rock province in eastern Shandong Province.[Methods]The petrography,major,trace and rare earth elements in whole rock,Sr-Nd-Pb isotope,zircon U-Pb dating and in-situ Hf isotope,X-ray diffraction and laser Raman spectroscopy,plagioclase electron probe and in-situ elemental scanning analysis of 8 samples obtained in the Xiaozhushan area were carried out,and the following conclusions were obtained.[Results]Petrography shows that the granite in the study area contains S-type granite characteristic mineral-cordierite,with pegmatite veins.The 10000 Ga/Al-Zr diagram shows the granite rock type,belong to I and S granite.All samples are high-silica granites(SiO_(2)>71.9%)with high total alkali content(Na_(2)O+K_(2)O>8.5),belonging to the highpotassium calc-alkaline series.Calculation of the index of highly fractionated granites:most samples with obvious Eu negative anomaly(δEu=0.4-0.5)and the aluminum saturation index is higher(A/CNK>1.2),the differentiation index(DI)is above 90,and the saturation temperature of zircon reflects the magma origin temperature is 832-875°C.Zircon Ti thermometer reflects that the crystallization temperature of magma is 618.8-726.44°C,which shows that magma differentiation experienced obvious cooling process.S-Nd-Pb isotopes show high I_(Sr) and lowε_(Nd)(t),indicates that the sample magma source area is crust.Geochronology shows tha

关 键 词：小珠山 岩石地球化学 高分异花岗岩 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]