江苏赣榆县石桥浅变质岩地球化学和锆石U-Pb年龄  

Geochemical characteristics and zircon U-Pb ages of low-grade metamorphic rocks in Shiqiao region, Ganyu County, Jiangsu Province

作　　者：袁亚娟[1,2] 夏斌[1,3] 张玉泉[1] 夏连泽[3] 李贺[1,2] 

机构地区：[1]中国科学院广州地球化学研究所,广东广州510640 [2]中国科学院大学,北京100049 [3]中山大学海洋学院,广东广州510275

出　　处：《地球化学》2013年第5期499-506,共8页Geochimica

基　　金：国家重点基础研究发展计划项目(2009CB219401);中国科学院知识创新项目(0734021)

摘　　要：对石桥浅变质岩进行了综合研究。结果表明：（1）岩石化学成分富碱（Na2O＋K2O6.39％～10.65％）、高钾、贫钠（Na2O／K2O=0.03-0.05）；（2）微量元素富集Rb、Ba、Th、U等大离子亲石元素和富Pb，贫Sr；（3）稀土元素含量为130.89～232.80gg／g，轻稀土元素富集（LREE／HREE=7.92～14.84），Eu负异常不明显（6Eu=0.73～0.911，模式曲线向右倾斜（La／Yb=8.4～21.3）；（4）锆石定年表明其时代属于寒武纪（554 Ma）；（5）变质复合锆石的老核，其年龄值较多的是在新太古代（2577～2502Ma）至古元古代（2500～1600Ma）。变质复合锆石的新壳，其年龄分别为2483、2370、2211、778和554Ma，表明继承锆石在其源区曾分别经过变质作用。前述特征均不同于大别一苏鲁超高压变质带的副片麻岩，暗示石桥浅变质岩的成因非原地，而是异地（飞来峰）。The low-grade metamorphic rocks in Shiqiao area are characterized by alkali-rich （Na2O＋K2O= 6.39%-10.65%）, high K20 （Na2O/K2O =0.03-0.05） and low Na20. They are further characterized by enrichment in 1 Rb, Ba, Th, Pb and U and depletion in Sr. The concentration of rare earth elements （REE） is in the range 130.89-232.80 μg/g. These rocks are enriched in light REE （LREE/HREE = 7.92-14.84） and lack of obvious Eu negative anomaly （δEu = 0.73-0.91）. The new shells of metamorphic composite zircon range in age from Proterozoic era （2483 Ma, 2370 Ma, 2211 Ma and 778 Ma） to Paleozoic era （544 Ma）. However, the existence of Paleozoic-age indicates the low-grade metamorphic rock within Shiqiao area belongs to the early Paleozoic （554 Ma）. The U-Pb ages of inherited zircons are concentrated at Mesoarchean, Neoarchean, Paleo-proterozoic. The different age within the news shells of metamorphic composite zircon shows that the inherited zircons were subjected to metamorphism in the source area. As the preceding feature are different from the paragneiss within Dabie-Sulu ultrahigh pressure metamorphic belt, the petrogenesis of the low grade metamorphic rock is a klippe.

关 键 词：锆石U-PB年龄 元素地球化学 浅变质岩 石桥 赣榆县 江苏省 

分 类 号：P597[天文地球—地球化学] P58[天文地球—地质学]