Geochronology and Geochemistry of Main Intrusions of the Gongqiongzuobo Fe-Cu Ore Occurrence in the Western Bangong Co–Nujiang Metallogenic Belt, Tibet and Its Geological Significance
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摘要: 本文对躬穷左波Fe-Cu矿区出露的三套酸性侵入岩进行了系统的LA-ICP-MS锆石U-Pb年代学和岩石地球化学研究.年代学测试结果显示花岗斑岩、二长花岗斑岩和钾长花岗岩206Pb/238U加权平均年龄分别为147.0 Ma、143.6 Ma和142.8 Ma,矿区存在晚侏罗世—早白垩世存在3期岩浆事件.岩石地球化学组成特征显示,花岗斑岩属准铝质-弱过铝质I型花岗岩;二长花岗斑岩为高钾钙碱性系列,属弱过铝质I型花岗岩;钾长花岗岩经历了强烈的结晶分异作用,属高分异I型花岗岩.岩石微量元素富集Rb、Th、U、Pb而亏损Nb、Ta、Ti、P元素,Nb/Ta比值接近大陆地壳组成及锆石负的εHf(t)值特征,指示成岩物质以壳源物质为主.躬穷左波晚侏罗世矽卡岩型Fe-Cu矿化事件的发现对于完善班—怒带西段成矿规律和指导区域找矿工作具有重要意义.Abstract: This paper reports systematic research about LA-ICP-MS zircon U-Pb age, whole-rock major and trace element of three acid intrusives from the Gongqiongzuobo Fe-Cu deposit. The result of Geochronology testing shows that the weighted average age are 147.0 Ma (Granite porphyry), 143.6 Ma (Monzonitic granite porphyry) and 142.8 Ma (K-feldspar granite) respectively and finds there are three periods of magma activity in Gongqiongzuobo area during Late Jurassic–Early Cretaceous Epoch. The result of geochemistry characteristics shows that (1)Granite porphyry belongs to aluminum-weakly peraluminous Ⅰ-type granite, (2)Monzonitic granite porphyry is high potassium calc-alkine series and belongs to weakly peraluminous Ⅰ-type granite, (3)K-feldspar granite has experienced strong crystallization differentiation and belongs to high differentiation Ⅰ-type granite. Those rocks enrich in Rb Th U Pb and deplete in Nb Ta Ti P, their Nb/Ta ratio are close to continental crust and the zircon has negativeεHf(t)value. All these feature implys rock-forming materials are mainly come from the crust-source. The discoveray of Late–Jurassic skarn-type mineralization has important significance for consummating regional metallogeny and directing regional prospecting.
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