CAJ | 학술논문

本文分析了西藏尼雄铁矿与成矿有关花岗闪长岩的主量元素、微量元素、稀土元素及Sr-Nd-Pb同位素特征,并做了锆石LA-ICPMS U-Pb年龄测定。岩石地球化学分析结果显示样品为亚铝质中钾–高钾钙碱性岩系列,属I-型花岗岩。地球化学组成上其富集大离子亲石元素(LILE)Rb、Ba、Sr、Th、U、K、Pb,亏损高场强元素(HFSE)Nb、Ta、Ti,具有典型的岛弧岩浆作用的特征；稀土元素球粒陨石标准化图解表现为富集轻稀土的右倾型式(LREE/HREE=5.67~8.37),无 Eu异常,显示活动大陆边缘岩浆岩的稀土配分特征。岩体ISr为0.707625~0.710997,εNd(t)为–6.6~–8.7,206Pb/204Pb,207Pb/204Pb,208Pb/204Pb 比值分别为18.786~18.955、15.694~15.726、39.355~39.676,显示出富集地幔特征(EMⅡ),表明地壳组分对岩浆生成有重要影响。所测岩体的锆石206Pb/238U 加权平均年龄为112.09±0.54 Ma(MSWD=0.45),表明尼雄花岗岩体形成于早白垩世晚期。综合分析班公湖–怒江中特提斯洋和雅鲁藏布江新特提斯洋的演化历史,作者认为尼雄铁矿是早白垩世雅鲁藏布江洋壳板块向北侧拉萨地块之下俯冲的构造背景下的产物。而成矿岩体主要是俯冲组分(流体和熔融)对地幔楔交代改造的结果,是地幔岩浆底侵引起下地壳物质部分熔融,两种岩浆混合而形成的。
본문분석료서장니웅철광여성광유관화강섬장암적주량원소、미량원소、희토원소급Sr-Nd-Pb동위소특정,병주료고석LA-ICPMS U-Pb년령측정。암석지구화학분석결과현시양품위아려질중갑–고갑개감성암계렬,속I-형화강암。지구화학조성상기부집대리자친석원소(LILE)Rb、Ba、Sr、Th、U、K、Pb,우손고장강원소(HFSE)Nb、Ta、Ti,구유전형적도호암장작용적특정；희토원소구립운석표준화도해표현위부집경희토적우경형식(LREE/HREE=5.67~8.37),무 Eu이상,현시활동대륙변연암장암적희토배분특정。암체ISr위0.707625~0.710997,εNd(t)위–6.6~–8.7,206Pb/204Pb,207Pb/204Pb,208Pb/204Pb 비치분별위18.786~18.955、15.694~15.726、39.355~39.676,현시출부집지만특정(EMⅡ),표명지각조분대암장생성유중요영향。소측암체적고석206Pb/238U 가권평균년령위112.09±0.54 Ma(MSWD=0.45),표명니웅화강암체형성우조백성세만기。종합분석반공호–노강중특제사양화아로장포강신특제사양적연화역사,작자인위니웅철광시조백성세아로장포강양각판괴향북측랍살지괴지하부충적구조배경하적산물。이성광암체주요시부충조분(류체화용융)대지만설교대개조적결과,시지만암장저침인기하지각물질부분용융,량충암장혼합이형성적。
Whole-rock major, trace and rare earth elements and Sr-Nd-Pb isotopic analyses, combined with zircon LA-ICPMS U-Pb dating, of granodiorite related to the Nixiong iron deposit, are carried out in this paper. The petrogeochemical analysis results indicate that the granodiorite related to Nixiong iron deposit belongs to subaluminous, medium-high K calc-alkaline I-type granite. Geochemically, the granodiorite is enriched in large ion lithophile elements(LILE) Rb, Ba, Sr, Th, U, K, Pb and depleted in high field strength elements(HFSE) Nb, Ta, Ti and shows basic characteristics of arc magmatic rocks. The rare earth element chondrite-normalized distribution patterns appear a notable enrichment of light rare earth elements relative to heavy rare earth elements without marked Eu anomalies and show signatures of magmatic rocks from an active continental margin. Zircon U-Pb LA-ICPMS dating yields a weighted 206Pb/238U mean age of 112.09±0.54 Ma with MSWD=0.45, indicating that the granodiorite was formed in late stage of Early Cretaceous. These granites have high radiogenic Sr isotopic ratios (ISr=0.707625–0.710997) and low Nd isotopic ratios εNd(t)(–6.6 to–8.7) and primitive Pb isotopic compositions (206Pb/204Pb=18.786–18.955, 207Pb/204Pb=15.694–15.726, 208Pb/204Pb=39.355–39.676), reflecting an important influence of crustal components on the magmatic generation. Through a comprehensive analysis on the evolution histories of the Bangonghu-Nujiang Meso-Tethyan ocean and the Yaluzangbo Neo-Tethyan ocean, the authors of the paper reach a conclusion that the Nixiong iron deposit is genetically related to the northward subduction of the Yarlu-Zangbo oceanic crust. The enrichment component of fluid and melt released from sediments adhered to the subducted oceanic crust triggered the mantle wedge partially melt to generate the enriched magma. The mantle magma intruded and caused partical melting of lower crust and mixed with each other to form the metallogenic magma.