山东省日照市岚山头片麻状碱性花岗岩的岩石地球化学、年代学和成因研究  

Dating and genesis study of the gneissic alkali granite in Lanshantou area,Shandong Province

作　　者：黄强太[1,3] 夏斌[1,2] 张玉泉[1] 蔡周荣[2] 夏连泽[2] 胡西冲[2] 

机构地区：[1]中国科学院广州地球化学研究所,广州510640 [2]中山大学,广州510275 [3]中国科学院研究生院,北京100049

出　　处：《地质科学》2013年第3期773-786,共14页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家“973”项目(编号:2012CB214705);国家自然科学青年基金项目(编号:41206035)资助

摘　　要：岚山头片麻状碱性花岗岩是由古生代的沉积岩变质而成,其主量元素具高硅(SiO_2=75%~77%)、富碱(Na_2O+K_2O=8.38%~8.60%)、低铝(Al_2O_3=11.72%~12.05%)、贫钙(CaO=0.09%~0.53%)等特征;其微量元素特征显示为,富集Rb、Ba、Th、U等大离子亲石元素和Pb,贫Nb、Ta、Zr、Hf、Ti等高场强元素,以及富集轻稀土(LREE/HREE=6.32~9.86)和铕负异常明显到中等(δ_(Eu)=-0.03~0.51)等;在研究锆石"CL"图像基础上,对具核—幔—壳3层结构的变质复合锆石的幔(第一次变质作用的产物),获得年龄为245 Ma和235 Ma,反映第一次超高压变质时间,也就是它的成岩时间,相当于早-中三叠世;变质复合锆石的新壳,年龄为222~198 Ma,第二次变质时间,也就是退变质作用的时间,相当于晚三叠世;对变质复合锆石老核"继承锆石"定年显示:既含有大量的属于元古代不同年龄段的岩浆碎屑锆石(864Ma^781 Ma^701 Ma^688 Ma^631 Ma^598 Ma^592 Ma),又含有比较多的属于古生代不同年龄段的岩浆碎屑锆石等(544 Ma^500 Ma^447 Ma^339 Ma^306 Ma),表明其寄主岩的时代不可能为元古代,只能是古生代。The field and indoor results show that the gneissic alkali granite from Lanshantou was converted from paleozoic sedimentary rock. Its chemical composition presents high Si（ SiO2 = 75%- 77%）,alkali-rich（Na20＋K20 = 8.38% - 8.60%）,1ow AI（A1203 = 11.72% - 12.05% ） ,and poor in Ca（ CaO = 0.09% - 0.53% ）. It was rich in the large-ion lithophile elements such as Rb,Ba,Th, U,Pb and poor in the high field strength elements such as Nb, Ta,Zr, Hf and Ti. The gneissie alkali granite presents relatively high LREE （ LREE/HREE = 6.32 - 9.86 ） elements and obviously Eu （SEu = 0.42 - 0.64 ） negative abnormality. Based on the base of studying the zircons CL images,The age of mantle of zircon with three-tier structure （core, mantle, shell ） is 245 Ma or 235 Ma which reflects the first ultra-high pressure metamorphic time and also is the time of forming of the gneissie alkali granite and equivalent to the Early-Middle Triassic. The age of new shell of metamorphic composite zircon is 222 - 198 Ma which reflected the second metamorphic time and equivalent to Late Triassic. The U-Pb dating results of old nuclear of metamorphic composite zircon reveal that the ages of magmatic and detrital zircons have both proterozoic era （864 Ma -781 Ma - 701 Ma -688 Ma - 631 Ma-598 Ma -592 Ma）and paleozoic era（544 Ma-500 Ma-447 bla -339 Ma- 306 Ma）. In summary, the ear of protolith of host rock can not be proterozoic and may be palaeozoic.

关 键 词：片麻状碱性花岗岩 地球化学和锆石年龄 山东日照岚山头 

分 类 号：P588[天文地球—岩石学] P597[天文地球—地质学]