摘要
吉林色洛河地区发育高镁安山岩类,SHRIMP锆石U-Pb定年结果表明它们形成于晚二叠世(252±5Ma)。色洛河高镁安山岩类(SiO_259.08%～65.67%)具有富MgO(3.68%～5.30%),高Mg~#值(0.62～0.68,平均0.66),高Cr(203.17×10^(-6)～379.70×10^(-6),平均258.79×10^(-6))、Ni(98.13×10^(-6)～249.35×10^(-6),平均137.00×10^(-6))含量;富集大离子亲石元素(如Cs、K、Pb、Rh和Ba),亏损高场强元素(如Ta、Ti、Nb、P);富集LREE(Ce39.14×10^(-6)～48.74×10^(-6)),强烈亏损HREE (Yb 0.95×10^(-6)～1.27×10^(-6),Y 10.80×10^(-6)～13.13×10^(-6),(La/Yb)_N13.27～16.66);但它们含有较低的Sr(158.62×10^(-6)～369.77×10^(-6),平均258.52×10^(-6))。它们属于中钾、钙碱性系列,具有明显的结晶分异和同化混染特征。上述地球化学特征表明它可能与消减沉积物流体交代形成富集地幔的部分熔融有关,其后又经历了分异和混染作用。这揭示它们形成于活动陆缘的构造背景,表明晚古生代末期古亚洲洋板块仍在消减,华北地块和佳木斯-兴凯地块(中亚造山带)最终的拼合时间可能在二叠纪之后。
High-Mg andesites occur in Seluohe, Jilin, China, which are dated at 252±5Ma by the SHRIMP zircon U-Pb method, indicating that they were generated in the Late Permian. The high-Mg andesites （ SiO2 59.08% - 65.67% ） are geochemically characterized by high MgO （3.68% -5.30 %） and high Mg^# （0.62 -0. 68, avg. 0.66） in association with enrichments of Cr （203.17 ×10^-6 -379.70×10^-6, avg. 258.79×10^-6） and Ni （98. 13×10^-6 -249.35×10^-6,avg. 137.00×10^-6）. These andesites are strongly enriched in light rare earth elements（ Ce 39.14×10^-6-48.74×10^-6） and large-ion-lithophile dements （such as Cs,K,Pb,Rb and Ba） , and are also characterized by depletion of high-field-strength dements （such as Ta,Ti ,Nb and P） and heavy rare earth elements （Yb0.95×10^-6-1.27 ×10^-6, Y 10.80×10^-6-13.13×10^-6, （La/Yb） N13.27-16.66）. In addition, the andesites have low Sr concentrations （ 158.62×10^-6 - 369.77×10^-6, avg. 258.52 × 10^-6 ）. Considering that the high-Mg andesites are a medium-K, calc-alkaline suite with assimilaton-fractional crystallization, it is suggested that Seluohe high-Mg andesites were most likely derived from the partial melting of enriched mantle wedge materials induced by hydrous fluid from subducted sediments in a subduction zone and then experienced assimilaton-fractional crystallization during ascending. It is thus concluded that Paleo-Asian ocean plate was presumably in the process of subduction during the late Permian, and the collision between North China and Jiamusi-Khanka plates might take place after the Permian.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第4期767-776,共10页
Acta Petrologica Sinica
基金
国家自然科学基金(40473030)
中国科学院知识创新工程(KZCXZ-104)
地质调查局(1212010561510)项目联合资助
