CAJ | 학술논문

通过对滇东北东川下田坝地区黑云母二长花岗岩和似斑状钾长花岗岩2种岩体的地球化学分析及对黑云母二长花岗岩的U-Pb同位素测试，得到如下认识：黑云母二长花岗岩和似斑状钾长花岗岩总体地球化学特征相似，主量元素表现出高SiO2（平均71.7%）、过铝质（A/CNK指数在1.03～1.52）的特征，过碱指数在0.95～1.37之间，总体属于钙碱系列；稀土元素总量较高（ΣREE平均313×10-6），（Ce/Yb）N均值为8.85，（La/Yb）N均值为9.54，呈现轻稀土元素（LREE）富集，仅Eu亏损（δEu均值0.31）的海鸥型右倾模式；大离子亲石元素Rb、Th、U、K等相对富集，高场强元素Nb、Ta、Sr、Ti等呈明显负异常，说明岩浆源岩以陆壳成分为主；Ga/Al均值为2.69，(Zr+Nb+Ce+Y)均值为383；微量元素Sr、Eu低，富集Nb、Zr等元素，反映其源区存在斜长石的残留；锆石饱和温度为724～786℃，表明初始岩浆温度较高。上述特征说明，下田坝花岗岩为典型的A型花岗岩，形成于中上地壳的板内伸展背景。黑云母二长花岗岩LA-ICP-MS锆石U-Pb年龄为801.1±6.6Ma，同时受到762.1±6.2Ma热事件的影响，与新元古代Rodinia超大陆裂解事件在时间上一致，亦与东川铜矿成矿时代相符，说明新元古代裂谷环境的岩浆事件范围可扩大至滇东北东川，并可能引发热液成矿作用。
통과대전동북동천하전패지구흑운모이장화강암화사반상갑장화강암2충암체적지구화학분석급대흑운모이장화강암적U-Pb동위소측시，득도여하인식：흑운모이장화강암화사반상갑장화강암총체지구화학특정상사，주량원소표현출고SiO2（평균71.7%）、과려질（A/CNK지수재1.03～1.52）적특정，과감지수재0.95～1.37지간，총체속우개감계렬；희토원소총량교고（ΣREE평균313×10-6），（Ce/Yb）N균치위8.85，（La/Yb）N균치위9.54，정현경희토원소（LREE）부집，부Eu우손（δEu균치0.31）적해구형우경모식；대리자친석원소Rb、Th、U、K등상대부집，고장강원소Nb、Ta、Sr、Ti등정명현부이상，설명암장원암이륙각성분위주；Ga/Al균치위2.69，(Zr+Nb+Ce+Y)균치위383；미량원소Sr、Eu저，부집Nb、Zr등원소，반영기원구존재사장석적잔류；고석포화온도위724～786℃，표명초시암장온도교고。상술특정설명，하전패화강암위전형적A형화강암，형성우중상지각적판내신전배경。흑운모이장화강암LA-ICP-MS고석U-Pb년령위801.1±6.6Ma，동시수도762.1±6.2Ma열사건적영향，여신원고대Rodinia초대륙렬해사건재시간상일치，역여동천동광성광시대상부，설명신원고대렬곡배경적암장사건범위가확대지전동북동천，병가능인발열액성광작용。
Geochemical analysis and LA-ICP-MS zircon U-Pb dating of Xiatianba granites of two granitic bodies in Dongchuan of northeast Yuannan were conducted in this study. The general geochemical characteristics of biotite adamellite and porphyraceous moy-ite are similar to each other, characterized by high SiO2(71.7% on average)and belonging to the peraluminous (A/CNK value be-tween 1.03~1.52) and alkaline series (AI value between 0.95~1.37). They have highΣREE content with an averageΣREE value of 313 × 10-6, an average(Ce/Yb)N value of 8.85, an average(La/Yb)N value of 9.54 and an average δEu value of 0.31. The chondirte-normalized REE patterns display right-oblique curves. The large ion lithophile elements, such as Rb, Th, U and K, are rel- atively enriched, whereas high HFSE such as Nb, Ta, Sr and Ti are relatively depleted, which indicates the existence of residual plagio-clase in the granite source area. Calculation also shows that the melt of Xiatianba granites was formed in an intraplate extension environ-ment with temperatures between 724℃and 786℃. These characteristics show that the Xiatianba granites are typical A-type granite. LA-ICP-MS U-Pb dating of zircon from biotite adamellite yielded a granite age of 801.1±6.6Ma (MSWD=0.84, n=14) and a ther-mal event age of 762.1 ± 6.2Ma (MSWD=0.72, n=14), which are highly in accordance with the time of breakup of Rodinia super-continent in the western Yangtze block, and are also consistent with the metallogenic epoch of the Dongchuan copper deposit, sug-gesting that the magmatism of the Neoproterozoic rift environment affected Dongchuan area and probably triggered hydatogenesis mineralization.