辽西建平杂岩中新太古代变质基性岩的地球化学、年代学及其地质意义

Geochemistry and Significance of the Neoarchean Meta-mafic Rock of Jianping Metamorphic Complex in Western Liaoning Province

在野外地质调查的基础上，对辽西建平杂岩中斜长角闪岩和基性麻粒岩进行了LA-ICP-MS锆石U—Pb同位素年代学和地球化学研究。结果显示，研究区新太古代末一古元古代初的变质年龄主要集中在2465～2453Ma，结晶年龄为～2593Ma。变基性岩原岩多属于拉斑玄武岩系列。两类岩石具有较高的A12O3含量（平均值14．49％）和较高的TiO，含量（平均值1．15％），与大洋玄武岩特征相似。样品Mg”变化较大（35—63），可能与岩浆上升过程中遭受地幔物质不同程度的混染有关。Ce／Yb—Ce图解反映了本区岩石样品起源于石榴子石二辉橄榄岩地幔。部分样品的轻、重稀土元素分馏程度相对较强（（La／Yb）N=5．67～10．87），同时具明显的Nb、rra、n负异常，与岛弧玄武岩的特征类似。平坦型稀土配分曲线显示正常型洋中脊玄武岩的特征。综合分析认为，本区新太古代末期基性岩浆作用形成于活动大陆边缘弧的构造背景下，并在稍晚的碰撞过程中发生变质作用，进而推断出新太古代末期研究区存在与现代板块类似的构造体制。

Based on the field work, LA-ICP-MS ziron U-Pb geochronology and geochemistry of the amphibolite and granulite from Jianping metamorphic complex in Western Liaoning Province, this study suggests that the metamorphic event of late Neoarchean and early Paleoproterozoic are mainly focused in 2 465 - 2 453 Ma and the age of crystallization is - 2 593 Ma. The two types of samples have relatively high A12 03 （ average is 14.49% ） and high TiO2 （ average is 1.15% ） , which are similar to the rocks originated from ocean basalt. Mg＂ values of samples have a larger variation （35 -63 ）which indicate that magma maybe contaminated by mantle substances during their ascent. Ce/Yb-Ce diagram reflect that samples stein from garnet lherzolite mantle. Am- phibolite and most granulites are characterized by enriched LREE （（La/Yb） N = 5. 67 ± 10. 87 ）, and obvious depletion of Nb, Ta, Ti, which is similar to that of island arc basah, while fiat curve has a character of N-type MORB. Comprehensive analysis shows that the mafic magmatism is formed in an active continental margin tee- tonic setting in the late Neoarchean, and then metamorphosed during the process of collision. So it is suggested that the study area exists a tectonic regime similar to modern plate in late Neoarchean.