摘要
柳洞岩体位于延边地区和龙市南部,大地构造位置上处于古洞河断裂西南侧,龙岗地块北缘,其岩性为二长花岗岩。为确定其侵位时代和大地构造环境,对柳洞岩体进行了系统的岩相学和年代学研究。N 6和N 7样品LA ICP MS锆石U Pb测年结果显示,其加权平均年龄分别为(118.63±0.69)Ma和(118.58±0.87)Ma。岩体具有高硅(w(SiO2)=70.30%~76.30%)、富碱(w(Na2O+ K2O)=7.82%~8.52%)、富铝(w(Al2 O3)=12.30%~15.50%)和低钛(w(TiO2)=0.16%~0.29%)的特点,属于高钾钙碱性系列。A/CNK值为1.03~1.11,为弱过铝质岩石。分异指数(D I)为87.99~94.89,固结指数(S I)为2.39~5.31,反映了该岩体经历了高程度分异演化作用。δEu为0.63~0.92,具有中等铕负异常,LREE/HREE和(La/Yb)N 值分别为3.46~8.09和10.59~33.94,显示轻稀土元素相对富集、重稀土元素亏损的特点。柳洞岩体明显富集Cs、Rb、Ba、K等大离子亲石元素(LILE),同时亏损 Nb、Ta、Ti等高场强元素(HFSE)以及P元素。综合岩相学、年代学、岩石地球化学特征及区域地质资料,柳洞岩体具有高分异的高钾钙碱性I型花岗岩的特点,形成于后造山向伸展转换的体制环境下。
The Liudong pluton is located in the southern Helong area of Yanbian area ,the southwest segment of Gudonghe fault and north margin of Longgang block .It’s composed of monzonitic granite . Systematic researches on petrography and geochronology have been carried out to determine the emplacement age and tectonic environment of the pluton .The LA ICP MS zircon U Pb dating yields the weighted mean age of (118 .63 ± 0 .69) Ma and (118 .58 ± 0 .87) Ma for N 6 and N 7 sample , respectively .The rock is weak peraluminous and belongs to the high potassium calc-alkaline series , characterized by high Si (70 .30% 76 .30% ) ,high alkali (7 .82% 8 .52% ) ,high aluminum (12 .30%15 .50% ) and low titanium (0 .16% 0 .29% ) ,with A/CNK value of 1 .03 1 .11 .Such geochemical characteristics as DI (87 .99 94 .89)and SI (2 .39 5 .31) indicate the rock experienced a highly fractionated evolving stage .The rock is of LREE enrichment (LREE/HREE=3 .46 8 .09) and HREE depletion ((La/Yb)N =10 .59 33 .94) .The Liudong pluton is characterized by the strong enrichment in large ion lithophile elements (LILE) ,such as Cs ,Pb ,Ba ,K ,depletion in high field-strength elements (HESE) ,such as Nb , Ta , Ti ,and P ,and middle negative Eu anomalies (δEu = 0 .63 ~ 0 .92) . Combining petrography , geochronology , rock geochemical characteristics , and regional geological material ,it can be concluded that the Liudong pluton belongs to the highly fractionated high-potassium calc-alkaline I-type granite and emplaced in the transferring stage from a post-orogenic to an extensional tectonic setting .
出处
《吉林大学学报(地球科学版)》
EI
CAS
CSCD
北大核心
2014年第1期145-157,共13页
Journal of Jilin University:Earth Science Edition
基金
国家自然科学基金项目(40972135
41272223)
中国地质调查局项目(1212011085481)