摘要
云南永平卓潘碱性杂岩体是金沙江-哀牢山富碱斑岩带中的重要岩体,位于兰坪走滑拉分盆地西部。该岩体的主要岩石类型为辉石正长岩、正长岩和霞石正长岩等。岩石地球化学显示高碱、高K_2O/Na_2O比值、低TiO_2、高Al_2O_3的超钾质钾玄岩系列岩石。微量元素表现为富集K、Rb、Sr、Ba等大离子亲石元素(LILE),亏损Ta、Nb、Ti、P、Zr等高场强元素(HFSE),表现为明显的"Ta-Nb-Ti"负异常,同时富集过渡性元素Cr、Ni、Co等。稀土元素为稀土总量高,富集LREE、(La/Yb)_N比值高、Eu异常不明显为特征。(^(87)Sr/^(86)Sr)_i比值为0.707611～0.709167、ε_(Nd)(t)值为-4.89～-6.57,^(206)Pb/^(204)Pb变化于18.6886～18.7022、^(207)Pb/^(204)Pb变化于15.6169～15.63493、^(208)Pb/^(204)Pb变化于38.7972～38.8927,显示岩浆源区具有富集地幔(EMⅡ)与下地壳共同作用的壳幔过渡带特征,构造环境判别为大陆弧(CAP)环境。岩体是在碰撞造山过程中大陆板片俯冲,使曾经遭受古洋壳板片流体强烈交代的壳幔过渡带在上升的软流圈熔体的注入而发生部分熔融,在走滑拉分盆地的核心部位沿构造断裂上升侵位而形成。
Zhuopan alkaline complex in Yongping, which located in western segment of strike-slip extensional basin of Lanping and mainly composed of gabbro-syenite, syenite and nepheline syenite, is predominant in alkali-rich porphyry zone of Jinshajiang-Ailaoshan. The complex is characterized by high alkaline, high K20/Na20, lower TiO2 and high Al2O3. Therefore, it belongs to Shoshonite. Trace elements are characterized by enrichments in K, Rb, Sr, Ba and other LILE, but strong depletion of Ta, Nb, Ti, P, Zr and other HFSE, significant Ta-Nb-Ti negative anomaly and high transitional elements. Chatracteristics of REE show high ∑ REE, high LREE abundance, high （La/Yb）N and weak Eu anomaly. （^87Sr/^86 Sr）i =0. 707611 -0. 709167, εNd（t） = -4. 89 -6.57, ^206Pb/^207 Pb -18. 6886 - 18. 7022, ^207 Pb/^204 Pb = 15. 6169 - 15. 63493, 2^208 Pb/^204 Pb = 38. 7972 - 38. 8927. These characteristics of Nd-Sr-Pb isotopes that the magma reservoir possesses the characteristics of crust-mantle transition between enrichment mantle and lower crust. Tectonic environment belongs to the continental arc. During the continental plate underthrust in collisional orogeny, crust-mantle transition which strongly metasomated by paleo-oceanic crust and infused by ascending asthenosphere is partially melted and the complex is emplaced in the core of the strike-slip extensional basin along the fractured zone.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第5期986-994,共9页
Acta Petrologica Sinica
基金
国土资源大调查综合研究项目(20001020026003)
国家重点基础研究发展规划"973"项目(2002 CB 412600)的资助
