鲁西泰山地区新太古代闪长岩及角闪石岩岩石成因及其对地壳演化的制约

泰山地区的闪长岩及角闪石岩与TTG片麻岩在空间上密切共生，是太古宙地体的重要组成部分，探究其母岩浆性质和岩石成因，对认识华北克拉通鲁西早期大陆地壳形成与演化具有重要意义。以泰山闪长岩和角闪石岩为研究对象，开展了详细的锆石U-Pb年龄、矿物化学和全岩-矿物Sr-Nd-Hf同位素研究。LA-ICP-MS锆石U-Pb定年结果显示，1件闪长岩和2件角闪石岩样品的207Pb/206Pb年龄加权平均值分别为2615 ±8 Ma、2627 ±14 Ma和2616 ±10 Ma，与全岩-矿物（角闪石和斜长石）Rb-Sr等时线定年得到的年龄结果（2621 ±7 Ma）一致，表明二者均属于新太古代约2.6 Ga岩浆作用的产物。2个岩体形成时代及矿物地球化学特征的相似性，表明它们应为同源岩浆不同演化阶段的产物，其母岩浆在后期上升侵位过程中受到分离结晶作用的影响，而率先形成的角闪石岩受分离结晶作用影响较小。利用角闪石的成分和已知的角闪石-熔体的分配系数计算得到的与闪长岩和角闪石岩中角闪石平衡的熔体表现为低Mg#值（平均值分别为31.9和43.4），富集Ba、Pb等大离子亲石元素，亏损Nb、Ta、Zr、Ti等高场强元素，以及具有平坦的重稀土元素配分型式。此外，岩石具有低的87Sr/86Sr初始值和接近亏损地幔的εNd（t）（-0.01~2.87）、εHf（t）（-0.76~4.89），且两阶段Nd模式年龄TDM2为2.97~2.73 Ga。综合来看，研究区闪长岩和角闪石岩的母岩浆可能来自于幔源岩浆底侵引起新生基性下地壳在角闪岩相条件下熔融形成的安山质母岩浆；该母岩浆经历了以斜长石、角闪石等矿物为主的结晶分异。鲁西地区在2.9~2.7 Ga经历了大规模的大陆地壳生长，新太古代晚期2.6~2.5 Ga经历了广泛的大陆地壳重熔再造，幔源岩浆的幕式底侵作用可能是华北克拉通新太古代早期（2.8~2.6 Ga）大陆地壳生长和分异的主要动力学原因之一。

Petrogenesis of the Neoarchean diorite and hornblendite in the Taishan area,western Shandong: Constraints on crustal evolution

The diorite and hornblendite associated with TTG gneisses constitute the important components of Precambrian metamorphic terranes in the Taishan area and their petrogenesis can provide significant insights into understanding the crustal growth and reworking events involving in the evolution of the North China Craton. The lithological, geochronological and geochemical analyses were carried out for the study of the representative diorite and hornblendite in the Taishan area. Zircon U-Pb dating of 1 diorite and 2 hornblendite samples yields 2615 ±8 Ma, 2627 ±14 M and 2616 ±10 Ma respectively, which are consistent with the emplacement age of 2621 ±7 Ma yielded from bulk rock-mineral Rb-Sr isochron dating. They are all magmatic products of the Neoarchean ~2.6 Ga. The similarity of the formation ages and mineral geochemical characteristics of the two intrusives indicates that they are the products of different evolution stages of the homologous magma. The parent magma experienced the influence of separation crystallization in the process of uplift and emplacement in the late stage, while the first hornblende was less affected by separation crystallization. Based on the composition of amphibole and the known amphibole melt partition coefficient, the melt in equilibrium with amphibole in diorite and amphibole is characterized by low Mg# value(mean value is 31.9 and 43.4, respectively), enrichment of large ion lithophile elements such as Ba and Pb, and depletion of high field strength elements such as Nb, Ta, Zr and Ti, and a flat distribution pattern of heavy rare earth elements. In addition, the rocks have a low initial 87Sr/86Sr value close to the εNd(t) value(-0.01~2.87) and εHf(t) value(-0.76~4.89) of the depleted mantle, and the two-stage Nd model age TDM2 ranges from 2.97 Ga to 2.73 Ga. On the basis of these data and in the context of the regional geology, it is inferred that the diorite and hornblendite were probably derived from the partial melting of juvenile mafic lower crust under the amphibolite facies conditions. The initial magma underwent crystallization differentiation of minerals such as plagioclase and hornblende. The west Shandong underwent extensive continental crustal growth at 2.9~2.7 Ga and extensive continental crustal remelting at 2.6~2.5 Ga in the late Neoarchean. The episodic diapirism of mantle derived magma might be one of the main dynamic causes for the growth and differentiation of the continental crust in the Early Neoarchean(2.8~2.6 Ga) of the North China Craton.