赞比亚北部省卡萨马西部石英闪长岩锆石U-Pb和Lu-Hf同位素及地球化学特征  

Zircon U-Pb geochronology, Lu-Hf isotopic compositions and geochemical characteristics of the quartz diorites from western Kasama in northern Zambia

作　　者：任军平[1] 王杰[1] 左立波[1] 古阿雷 孙宏伟[1] 许康康[1] CHIPILAUKA Mukofu ALPHET PHASKANI Dokowe EZEKIAH Chikambwe CHISHIMBA Canisius DANIEL Malunga REN Junping;WANG Jie;ZUO Libo;GU Alei;SUN Hongwei;XU Kangkang;CHIPILAUKA Mukofu;ALPHET PHASKANI Dokowe;EZEKIAH Chikambwe;CHISHIMBA Canisius;DANIEL Malunga(Tianjin Center China Geological Survey,Tianjin,300170,China;Geological Survey Department of Zambia,P.O.Bot.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]赞比亚地质调查局,赞比亚卢萨卡,P.O.Box.50135

出　　处：《地质学报》2019年第11期2832-2846,共15页Acta Geologica Sinica

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

摘　　要：石英闪长岩锆石U-Pb和Lu-Hf同位素及地球化学特征研究对赞比亚东北部班韦乌卢地块的形成时代及构造演化具有重要的研究意义。采用LA-MC-ICP MS方法测得班韦乌卢地块中卡萨马西部地区出露的两个石英闪长岩体中锆石的207Pb/206Pb年龄加权平均值分别为1964±8 Ma(MSWD=0.87,N=32)和1913±10 Ma(MSWD=0.77,N=19),表明两期石英闪长岩均形成于古元古代且可能与古元古代乌本迪构造带的活动有关。全岩地球化学分析显示,石英闪长岩属准铝质、高钾钙碱性系列岩石。稀土配分曲线均呈右倾型,具有富含轻稀土元素(LREE)、贫重稀土元素(HREE)以及δEu(0.77~0.80)弱负异常特点。微量元素均显示大离子亲石元素(如Rb、Ba及K)和活泼的不相容元素(如Th及U)相对富集,高场强元素Nb、Ta、P、Sr和Ti相对亏损。Nd/Th=3.60~4.65,Nb/Ta=12.05~13.87,Th/Ta=11.14~11.81,Ti/Zr=36.84~41.71,Ti/Y=220.28~300.00和具有不均一的εHf(t)值(分别为-3.8~1.3和-4.3~8.6)均显示石英闪长岩的原始岩浆具有壳幔混合的特点。Zr/Y=5.98~7.19,La/Nb=2.91~3.88,La/Yb=12.19~13.92及构造判别图解均显示石英闪长岩形成于安第斯型活动大陆边缘。Zircon U-Pb geochronology, Lu-Hf isotopic compositions and geochemistry characteristics of the quartz diorites are always used to reveal tectonic activities and evolutions of the Bangweulu Block. The zircon LA-MC-ICP MS U-Pb dating results of the quartz diorites show that their weighted 207Pb/206U age is 1964±8 Ma(MSWD=0.87, N=32) and 1913±10 Ma(MSWD=0.77, N=19), respectively, indicating that the intrusions of the quartz diorites intruded in the Palaeoproterozoic and have a good relation with the Paleoproterozoic Ubendian Belt. The whole-rock geochemical analysis results show that the quartz diorites are metaluminous and belong to the high-calc-alkaline series. The rare earth elements chondrite standardized curves show that they are rich in light REE and deplete in heavy REE with weak negative δEu(0.77~0.80). The quartz diorites are enriched in LILE(such as K, Ba and Rb), LREE and more mobile incompatible elements(such as Th and U), relatively depleted in HFSE(such as Nb,Ta, P, Sr and Ti). Nd/Th of 3.60~4.65, Nb/Ta of 12.05~13.87, Th/Ta of 11.14~11.81, Ti/Zr of 36.84~41.71, Ti/Y of 220.28~300.00 and variable εHf(t) values of-3.8 to 1.3 and-4.3 to 8.6 suggest that the origin of the quartz diorites was a mixture of crust-mantle. Zr/Y of 5.98~7.19, La/Nb of 2.91~3.88, La/Yb of 12.19~13.92 and geotectonic discriminant diagrams show that the quartz diorites formed in an Andean-type active continental margin setting.

关 键 词：石英闪长岩 锆石U-Pb和Lu-Hf同位素 地球化学 卡萨马西部 班韦乌卢地块 赞比亚东北部 

分 类 号：P61[天文地球—矿床学]