鲁西下常庄中三叠世磁铁角闪岩的岩石地球化学和Sr-Nd同位素:对岩石成因和构造背景的制约  

Geochemistry and Sr-Nd isotope compostions of Middle Triassic Xiachangzhuang magnetite amphibolites from western Shandong:constraints on petrogenesis and tectonic setting

作　　者：师江朋 霍腾飞[1] 杨浩田[1] 杨德彬[1] 王清海[2] 刘金民 SHI Jiang-peng;LIU Jin-min;HUO Teng-fei;YANG Hao-tian;YANG De-bin;WANG Qing-hai(College of Earth Sciences, Jilin University, Changchun 130061, China;International Center for Geoscience Research and Education in Northeast Asia, Jilin University, Changchun 130026, China;Bureau of Geology and Mineral Resources of Shandong Province, Ji’nan 250013, China)

机构地区：[1]吉林大学地球科学学院,长春130061 [2]吉林大学东北亚国际地学研究与教学中心,长春130026 [3]山东省地质矿产局,济南250013

出　　处：《世界地质》2016年第3期608-616,共9页World Geology

基　　金：新世纪优秀人才支持计划(NCET-12-0237);国家自然科学基金(41472052);中央高校基本科研业务费联合资助

摘　　要：下常庄中三叠世(242Ma)磁铁角闪岩的岩相学、岩石地球化学和Sr-Nd同位素的研究结果表明,下常庄磁铁角闪岩主要由角闪石(40%~45%)、磁铁矿(35%~45%)和斜长石(10%~15%)及少量的单斜辉石(1%~3%)组成;具低的SiO_2(24.25%~38.40%)、K_2O(0.02%~1.09%)和Na_2O(0.16%~1.68%)含量,较高的MgO(6.86%~11.81%)、Fe_2O_3~T(21.69%~36.62%)和TiO_2(7.37%~13.46%)含量;轻稀土元素(LREE)相对富集、重稀土元素(HREE)相对亏损(∑LREE/∑HREE=7.09~8.97、(La/Yb)_N=10.67~16.62),无明显的Eu异常(δEu=0.83~1.01);富集大离子亲石元素(Rb、Ba、Sr),高场强元素(Nb、Ta、Zr、Hf)不亏损,具Pb和Ti的正异常;全岩^(87)Sr/^(86)Sr初始比值介于0.702 645~0.706 534之间,ε_(Nd)(t)值变化于-7.51^-12.59之间,T_(DM1)=2 374~2 413 Ma。上述结果暗示,下常庄磁铁角闪岩的原岩可能为角闪辉长岩,起源于受下地壳物质混染的华北地块富集岩石圈地幔的部分熔融。下常庄中三叠世磁铁角闪岩原岩的形成时代与大别—苏鲁高压-超高压变质的峰期时间一致,暗示它们可能形成于中生代早期洋壳俯冲-消减向陆-陆碰撞造山转换的构造背景。The systematically petrographical, geochemical and Sr-Nd isotopic research of the Middle Triassic Xiachangzhuang magnetite amphibolites (242 Ma) show that they are mainly composed of hornblende ( 4 0 % ~4 5 % ) , magnetite ( 3 5 % ~4 5 % ) , plagioclase ( 1 0 % ?1 5 % ) and clinopyroxene (1 % ?3 % ) . The magnetite amphibolites have low contents of Si0 2 (24. 2 5 % ?38. 4 0 % ) ,K20 (0? 0 2 % ?1. 0 9 % ) ,Na20 (0? 1 6 % ?1. 6 8 % ) , and high concentrations of MgO (6. 8 6 % ?11. 8 1 % ) ,Fe2〇J (21. 6 9 % ?36. 6 2 % ) ,Ti0 2 (7. 3 7 % ?13. 4 6 % ) . They are enriched in light rare earth elements (LREEs) and depleted in high field strength elements (HREEs) ( SLREE/ ;IH R E E =7. 09 ?8. 97) with high (La/ Yb)Nvalues (10. 67 ?16. 62) and weak negative Eu anomaly (5Eu = 0. 83 ?1. 01) . Additonally, they are enrichment of LILEs (Rb, Ba and Sr) , nondepletion of HFSEs (Nb, Ta, Zr and Hf) , and show normal Pb and Ti anomalies. The whole-rock 87Sr/86Sr initial ratios range from 0. 702 645 to 0. 706 534, corresponding to s m (t) and model ages ( r DM1) ranging from -7. 51 to - 12. 59 and 237 4 to 2 413 Ma, respectively. The above results suggest that the protolith of the Xiachangzhuang magnetite amphibolites may be hornblende gabbros derived dominantly from partial melting of enriched lithospheric mantle of North China Block. The forming age of the Middle Triassic Xiachangzhuang magnetite amphibolites is similar to the peak period age of the Dabie -Sulu UHP metamorphism, which suggests that they might form in a transformation tectonic setting changing from ocean-continent subduction to the continent-continent collision in Early Mesozoic.

关 键 词：三叠纪 磁铁角闪岩 岩石成因 下常庄 华北地块 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]