赞比亚北部卡帕图地区古元古代花岗岩成因:岩石地球化学、锆石年代学及Hf同位素约束  

Petrogenesis of the Paleoproterozoic granitoids in Kapatu,northern Zambia:constrains from geochemistry,zircon U-Pb chronology and Hf isotopes

作　　者：古阿雷 王杰[1] 任军平[1] 左立波[1] 孙宏伟[1] 吴兴源[1] 邢仕 刘子江 张金达 EZEKIAH Chikambwe EVARISTO Kasumba GU Alei;WANG Jie;REN Junping;ZUO Libo;SUN Hongwei;WU Xingyuan;XING Shi;LIU Zijiang;ZHANG Jinda;EZEKIAH Chikambwe;EVARISTO Kasumba(Tianjin Center,China Geological Survey,Tianjin,300170,China;No.5 Geological Team,Bureau of Geologic Exploration and Mineral Development of Hebei Province,Tangshan,Hebei,063000,China;Geological Survey Department of Zambia,P.O.Box.50135 Lusaka,Zambia)

机构地区：[1]中国地质调查局天津地质调查中心,中国天津300170 [2]河北省地矿局第五地质大队,中国唐山063000 [3]赞比亚地质调查局,赞比亚卢萨卡P.O.Box.50135

出　　处：《地质学报》2021年第4期999-1018,共20页Acta Geologica Sinica

基　　金：商务部技术援外项目([2012]558和[2015]352);中国地质调查局项目(编号DD20201150,DD20190439和1212011220910)资助的成果。

摘　　要：赞比亚北部地区广泛发育古元古代花岗岩,是研究班韦乌卢地块构造岩浆作用特征的天然实验室。本文对赞比亚北部卡帕图地区大面积出露的花岗岩体开展较系统的岩相学、岩石地球化学、锆石U-Pb年代学和Hf同位素研究。结果显示,卡帕图地区主体花岗岩形成于2012±11~1970±20Ma,晚期浅肉红色似斑状正长花岗岩侵位年龄为1959±16Ma,均为古元古代岩浆活动,大量太古宙捕获锆石信息显示班韦乌卢地块可能存在太古宙地壳组分残留。地球化学数据表明,卡帕图花岗岩具有高硅(SiO_(2)=67.93%~72.80%)、高铝(13.85%~14.91%)、富钾(Na_(2)O/K_(2)O=0.29~0.89)、低镁(0.38%~1.93%)、低磷(0.10%~0.23%)的特点,铝饱和指数A/CNK在1.04~1.19之间,CIPW刚玉标准分子指数大于1%(1.01%~2.51%);稀土元素分配模式整体右倾,其中主体花岗岩稀土含量较高(ΣREE=191.79×10^(-6)~294.25×10^(-6)),Eu负异常(δEu=0.26~0.53),晚期浅肉红色似斑状正长花岗岩稀土含量相对较低(ΣREE=48.58×10^(-6)~54.00×10^(-6)),Eu弱正异常(δEu=1.04~1.37);微量元素中,卡帕图花岗岩富集Rb、K等大离子亲石元素,亏损Ba、Sr和高场强元素Nb、Ta等,并具有较低的Cr(3.56×10^(-6)~65.6×10^(-6))、Co(1.99×10^(-6)~12.5×10^(-6))和Ni(2.16×10^(-6)~33.7×10^(-6))含量;以上特征表明研究区古元古代花岗岩属于S型花岗岩。Hf同位素结果表明,卡帕图花岗岩的εHf(t)值和二阶段模式年龄tDM2值分别介于-15.9~+4.7和2289~3596Ma,远大于其锆石的结晶年龄,指示岩浆源区成分的强不均一性,岩浆源区系太古宙-古元古代陆壳部分熔融产物,存在不同程度的地幔物质混入。此外,主体岩石较高的CaO/Na_(2)O和低的Rb/Sr比值,表明主体花岗岩原岩是由地壳砂质岩部分熔融而来;晚期浅肉红色似斑状花岗岩低的CaO/Na_(2)O和高的Rb/Sr比值,指示泥质岩源区熔融。综合区域和全球构造演化历史,本次研究认为卡帕图花岗岩形成于坦Paleoproterozoic granite is widely exposed in northern Zambia,which is a natural laboratory for studying the magmatism and tectonic evolution in the Banweulu block.In this paper,systematic studies of petrology,LA-MC-ICP-MS zircon U-Pb geochronology,petrogeochemistry and Lu-Hf isotopes were conducted on the exposed granites in Kapatu area,northern Zambia.The results show that the main granites in the Kapatu area were formed between 2012±11~1970±20 Ma,and the emlocation age of the late shallow-flesh-red porphyritic syenogranite was 1959±16 Ma,both of which were paleoproterozoic magmatic activities.A large number of Archean captured zircons show that there may be remnants of Archean crustal components in the Bangweulu block.The Kapatu granites have high SiO_(2)(67.93%~72.80%),high aluminum(13.85%~14.91%),high Na_(2)O/K_(2)O(0.29~0.89),low MgO(0.38%~1.93%),and low P_(2)O_(5)(0.10%~0.23%).A/CNK values range from 1.04~1.19,and the CIPW corundum standard molecular index is greater than 1%(1.01%~2.51%).The chondrite-normalized REE patterns of the granites show right oblique.The main granites have relatively high total rare earth elements(ΣREE=191.79×10%(-6)~294.25×10^(-6))with evidently negative Euanomalies(δEu=0.26~0.53),where as the late shallow-flesh-red porphyritic syenogranites have relatively low total rare earth elements(ΣREE=48.58×10^(-6)~54.00×10^(-6))with positive Eu anomalies(δEu=1.04~1.37).The Kapatu granites were enriched in large-ion lithophile elements(LILEs)(e.g.Rb,K),but depleted in Ba,Sr and high-field-strength elements(HFSEs)(e.g.Nb,Ta),and have low Cr(3.56×10^(-6)~65.6×10^(-6)),Co(1.99×10^(-6)~12.5×10^(-6)),and Ni(2.16×10^(-6)~33.7×10^(-6)).The above results show that the Paleoproterozoic granites belong to S-type granites.Hf isotopic results show that theεHf(t)values and two-stage Hf model age(tDM2)values were-15.9~+4.7 and 2289~3596 Ma,respectively,far older than the crystallization age of zircon,indicating strong heterogeneity in the composition of the magma source,which was deriv

关 键 词：古元古代 S型花岗岩 班韦乌卢地块 卡帕图地区 赞比亚北部 

分 类 号：P597.3[天文地球—地球化学] P588.121[天文地球—地质学]