摘要
华北克拉通东北缘龙岗第四纪玄武岩的地球化学研究为大陆碱性玄武岩的成因以及源区的性质提供了重要的依据。龙岗第四纪玄武岩为碱性玄武岩,具有类似 OIB 的 REE 和微量元素分配特征。岩石的 Sr-Nd 同位素轻度亏损(^(87)Sr/^(86)Sr=0.7044～0.7048,ε_(Nd)=0.6～2.1),具有 Dupal 异常的高放射性成因 Pb 同位素组成(^(206)Pb/^(204)Pb:17.734～18.194,^(207)Pb/^(204)Pb=15.553～15.594,^(208)Pb/^(204)Pb=38.322～38.707)。这种地球化学特征指示了原始岩浆起源于<70km 深度的地幔,并经历了一定程度的橄榄岩、单斜辉石和钛-铁氧化物的结晶分异。岩浆源区中以来类似 MORB 软流圈物质的熔体为主,另外有少量来自 EM Ⅰ性质的富集岩石圈地幔以及俯冲流体/熔体的物质贡献,显示了深部岩石圈-软流圈一定程度的相互作用以及太平洋板块俯冲的影响。岩浆源区多种端元组分的存在表明该地区岩石圈的减薄/置换受到多种因素的影响。
The geochemistry of Quaternary volcanic rocks from Longgang provides important constraints on the petrogenesis of continental alkali basalts and characteristics of mantle source in the eastern North China Craton. Longgang Quaternary basalts are alkali affinities and characterized by OIB-like REE and trace elements patterns. Longgang basalts show slight depleted Sr-Nd isotopic compositions （^87 Sr/^86 Sr = 0. 7044 - 0. 7048, εNd = 0. 6 - 2. 1 ） and Dupal-like Pb isotopic compositions （^286 Pb/^284 Pb = 17. 734 - 18. 194, ^207 Pb/^204Pb = 15. 553 - 15. 594, ^208 Pb/^204Pb = 38. 322 - 38. 707）. These integrated geochemical and isotopic signatures consist with mantle mixing between MORB-like asthenospheric mantle, isotopically enriched EM I -type subcontinental lithospheric mantle and fluid/melt derived from subducted slab, indicating some degree interaction between lithosphere and asthenosphere and influence of subduction of the Pacific plate. The existing of multiple end-members in the magma source suggests that there might be several factors which affect the process of the lithospheric thinning or replacement in this region.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第6期1413-1422,共10页
Acta Petrologica Sinica
基金
国家自然科学基金(编号:40472031)项目资助
