机构地区: 中山大学海洋学院
出 处: 《地质科学》 2014年第1期214-225,共12页
摘 要: 通过野外和室内研究结果表明,石桥片麻岩是由沉积岩变质组成。在化学成分上,表现为高硅(Si02=75.22%~76.42%)、低铝(A1203=11.02%~12.29%)、富碱(Na20+K20=8.00%,8.68%)和贫钙(CaO=0.30%~0.82%),富集Rb、Ba、Th、U等大离子亲石元素,贫Nb、Ta、zr、Hf、Ti等高场强元素,以及轻稀土相对富集(LREE/HREE=6.06~7.14)、铕负异常较明显(8Eu=0.18~0.56)等。通过锆石成因类型及定年研究,获得超高压变质作用时间为254Ma和退变质作用时间为217Ma,老核(继承锆石)岩浆碎屑锆石是异地多时代(元古代一古生代),其寄主岩的原岩为沉积岩,时代不会早于古生代。 The gneiss in Shiqiao area are characterized by high SiO2( SiO2 = 75.22%-76.42% ) , low AlzO3(A1203 = 11.02%- 12.29%) , alkali-rich( Na20+K20 = 8.00%- 8.68%) and low CaO ( CaO = 0.30%- 0. 82%). They are further characterized by enrichment in large-ion lithophile elements such as Rb,Ba,Th and U and depletion in high field-strength elements such as Nb, Ta, Zr, Hf and Ti. The concentration of rare earth elements(REE) is in the range 170.51x 10-s -263.49~10-6. These rocks are enriched in light REE( LREE/HREE = 6.06-7.14) and lack of obvious Eu negative anomaly(6Eu=0.18-0. 56). We yield the zircon U-Pb age of 254 Ma corresponding to the UHP time,and 217 Ma are retrograde time. Above all,a large number of allochthonous inherited zircon are formed in different times,which indicates the original rock of the Shiqiao gneiss should be sedimentary rocks and it may not be earlier than the Paleozoic era.