滇西北衙煌斑岩的岩石成因及动力学背景：年代学、地球化学及Sr-Nd-Pb-Hf同位素约束  

Genesis and geodynamic settings of lamprophyres from Beiya,western Yunnan: Constraints from geochemistry,geochronology and Sr-Nd-Pb-Hf isotopes

作　　者：和文言[1] 莫宣学[1] 喻学惠[1] 董国臣[1] 和中华[2] 黄雄飞[1] 李小伟[1] 姜丽莉[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室地球科学与资源学院,北京100083 [2]云南黄金矿业集团股份有限公司,昆明650224

出　　处：《岩石学报》2014年第11期3287-3300,共14页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划项目(2015CB452605、2009CB421002);中国地质调查局地质调查工作项目(132120114013501);地质过程与矿产资源国家重点实验室开放基金(GPMR2011);国土资源部公益性行业科研专项(200911007-3);中国博士后科学基金(2014M550081);国家自然科学基金项目(41403028)联合资助

摘　　要：北衙地区出露有多条煌斑岩脉,锆石LA-ICP-MS定年表明岩脉的侵位时间为34.96±0.66Ma,与滇西地区新生代岩浆活动的高峰期一致。岩石地球化学分析表明北衙煌斑岩具有高钾(K2O/Na2O为1.03~10.38)、富碱((K2O+Na2O)(平均7.55%)、高Mg#(30~73),富集大离子亲石元素(LILE)(K、Rb、Ba)和轻稀土元素(LREE),亏损高场强元素(HFSE)和重稀土元素的特征。同位素以高(87Sr/86Sr)i(0.70615~0.70825),低εNd(t)(-5.3^-1.3),富集放射性Pb(208Pb/204Pb=38.542~38.856,207Pb/204Pb=15.553~15.617,206Pb/204Pb=18.482~18.612)为特征,176Hf/177Hf为0.282631~0.282882,εHf(t)为-4.2~1.8。岩石地球化学和同位素特征表明该煌斑岩源自经俯冲板片交代富集了的岩石圈地幔,推测源区可能为含金云母的尖晶石相橄榄岩地幔与石榴石相橄榄岩地幔的过渡区,起源深度大致在75~85km,明显高于同区富碱斑岩的起源深度。构造和地球动力学背景分析表明,该煌斑岩以及滇西地区新生代岩浆作用都是对印度-欧亚大陆强烈碰撞的响应,都产在强烈伸展的动力学背景下,为岩石圈减薄的产物。Quite a few lamprophyre dikes are developed in Beiya area. Zircon LA-ICP-MS U-Pb dating yields an age of 34. 96 ±0. 66 Ma,which indicate it is the product of Cenozoic magmatism in the Jinshajiang-Ailaoshan alkali-rich intrusion belt. Geochemically,the lamprophyres have high values of potassium（ K2 O / Na2 O ratio ranging from 1. 03 to 10. 38）,alkaline（ the content of（ K2 O ＋Na2O） mean value 7. 55%） and Mg^#（ from 30 to 73） and are enriched in large ion lithophile elements（ K,Rb,Ba） and LREEs and depleted in the high field strength elements（ Nb,Zr,P） and HREE. The isotopes of lamprophyres are characterized by high（87Sr /86Sr）i（ from 0. 707615 to 0. 708525）,low εNd（ t）（ from- 5. 3 to- 1. 3） but enriched radioactive Pb（208Pb /204 Pb = 38. 542 ~38. 856,207 Pb /204 Pb = 15. 553 ~ 15. 617,206 Pb /204 Pb = 18. 482 ~ 18. 612）. The ratios of176 Hf /177 Hf range from 0. 282631 to0. 282882,with εHf（ t） values varying from- 4. 2 to 1. 8. Based on the above discussions,we proposed that the studied lamprophyres are from an enrichment lithospheric mantle source which is metasomatized by the fluid from the dehydration of the subducted oceanic（ Paleo-Tethys Ocean） slab. There is fractionation of olivine and clinopyroxene with the primary magma ascent,but without much influence. Tectonic and geodynamic investigation indicates that the studied lamprophyres are formed in a post-orogenic extensional setting after the collision between the collision between Indian and Eurasian plate.

关 键 词：煌斑岩 地球化学 年代学 Sr-Nd-Pb-Hf同位素 滇西北衙 

分 类 号：P588.13[天文地球—岩石学] P597.3[天文地球—地质学]