【摘要】 嵩山地区登封群是华北克拉通南部古老结晶基底的重要组成部分,由一套火山-沉积成因的表壳岩系组成,形成于新太古代。斜长角闪质岩石广泛发育于登封群表壳岩中,同时,也以包体形式普遍存在于TTG片麻岩体内部。二者主量元素差别不大,SiO₂含量为45%～63%,富Fe₂O₃、Al₂O₃、CaO,TiO₂（0.5%～1.11%）含量较低,原岩为亚碱性玄武岩、安山岩。二者的微量元素特征稍有差别,登封群斜长角闪岩REE配分形式平坦,轻重稀土基本无分异（（La/Yb）_N=0.99～2.07）,基本无Eu异常（δEu≈1）;Ti负异常,Nb、Ta、Y负异常不明显,Ba、Sr呈现正异常,显示洋中脊和岛孤拉斑玄武岩特征;在Cr-Y、Ta/Yb-Th/Yb、Zr/Y-Nb/Y图解中位于洋中脊向岛孤玄武岩的过渡区域;ε_Nd（t）=4.43,显示源岩来自亏损地幔。而TTG片麻岩中斜长角闪岩包体的LREE富集,Eu负异常明显（δEu=0.46～0.87）;大离子亲石元素Rb、Cs、Ba明显高于登封群中的斜长角闪岩,除了Ti含量稍低外,Zr、Nb和Y含量范围和登封群斜长角闪岩相似,Nb、Ta和Y呈负异常,具有岛弧玄武岩特征;ε_Nd（t）=2.56和4.08,显示源岩来自亏损地幔,反映有地壳物质的混染。登封群斜长角闪岩及斜长角闪岩包体原岩的源区物质有所不同,在汇聚板块边缘洋壳俯冲条件下,前者是地幔楔部分熔融的产物,形成于弧后盆地环境;后者可能是随着俯冲作用的进行,小部分板片熔融开始发生,形成的熔浆混染亏损地幔部分熔融形成的熔浆。地球化学特征显示登封群形成的地球动力学背景是汇聚板块边缘洋壳的俯冲,反映当时陆壳以水平方式增生。更多还原

【Abstract】 The Dengfeng Group in Songshan area is a part of the ancient crystalline basement in the southern part of the North China Craton.The Group mainly consists of metamorphosed volcanogenic and sedimentogenic supracrustal rocks,in which the amphibolite is a very common type.The amphibolite includes two types which occur as rock body in Dengfeng Group and as enclaves in TTG gneiss, respectively.Both types have similar major components,they are all rich in Fe₂O₃,Al₂O₃ and CaO but poor in TiO₂（ranging from 0.50%to 1.11%）,and have SiO₂ content ranging from 45%to 63%.These features indicate that they are orthometamorphite and are similar to sub-alkaline basalts and andesite.Nevertheless,the trace and rare earth element characteristics of amphibolites body in Dengfeng Group and amphibolites enclaves in TTG gneiss are different,the former has relatively flat REE pattern（（La/Yb）_N is from 0.99 to 2.07） with no Eu anomalies（δEu is about 1） on the chondrite-normalized REE patterns,and exhibit negative Ti but positive Ba and Sr anomalies with slightly negative Nb,Ta and Y anomalies on the primitive-mantle normalized spidergrams,similar to MORB and island arc tholeiite.The whole rock Nd isotopic compositions(ε_Nd（t） is 4.43) of the amphibolite body indicate that they may originate from a depleted mantle.In contrast,the enclaves in TTG gneiss have relatively higher HREE/HREE ratios with negative Eu anomalies（δEu=0.46 to 0.87）.It has higher Rb,Cs and Ba contents but lower Ti content than the amphibolites body,and exhibits negative Nb,Ta and Y anomalies,similar to island arc basalts.The whole rock Nd isotopic compositions(ε_Nd（t） are 2.56 and 4.08) indicate that the enclaves may originate from a depleted mantle with the assimilation of older crust.We propose that the amphibolite body in Dengfeng Group may have formed by partial melting of mantle wedge in a subduction zone and erupted through the back-arc basin,whereas the enclaves in TTG geniss may have formed by partial melting of mantle wedge with assimilation of melts formed by slight partial melting of subducted oceanic slab.The geochemical characteristics of the both types of amphibolites indicate that the geodynamic background of Dengfeng Group is oceanic slab subducting in a convergent plate margin,reflecting that the continent crust in the Neo-Archean could grow in a parallel way.更多还原