Abstract

On the basis of the available geochronological data, the main stages of formation of Archean rocks belonging to the tonalite-trondhjemite-granodiorite (TTG) association, with ages of about 3240, 3150, 2900, 2850, 2800, and 2750 Ma, are identified and characterized within the Karelian Province of the Fennoscandian Shield. The distinctive features of geological positions and chemical compositions of TTG rocks of different stages are shown. For example, early TTG melts could have been melted not from basalts of the greenstone belts of the Karelian Province, but from lower crustal basites or from early amphibolites of the Vodlozero domain. Features of the geological position, chemical composition, and ε_Nd(t) isotopic evolution do not support the assumption that most of the TTGs formed from tholeiites of the greenstone belts, thus excluding their genetic connection with subduction of the ancient oceanic crust. The most acceptable model seems to be the formation of TTGs in the Karelian Province as a result of plume-affected melting of lower crustal mafites. Archean TTGs differ markedly from Phanerozoic plagiogranitoids not only in the shape and size of the massifs but also in a number of geochemical features, in particular, lower HREE, Sc, Y, and Ti contents.

中文翻译：

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卡累利阿省太古宙闪长岩-Trondhjemite-花岗闪长岩组合：地质、地球化学、形成阶段和条件

摘要

根据现有的年代学资料，确定了属于英云长岩-长长花岗岩-花岗闪长岩（TTG）组合的太古代岩石的主要形成阶段，年龄约为 3240、3150、2900、2850、2800 和 2750 Ma并且在芬诺斯坎迪亚地盾的卡累利阿省内具有特征。显示了不同阶段TTG岩石的地质位置和化学成分的显着特征。例如，早期的 TTG 熔体可能不是来自卡累利阿省绿岩带的玄武岩，而是来自下地壳基岩或 Vodlozero 域的早期角闪岩。地质位置、化学成分、_εNd特征(t) 同位素演化不支持大多数 TTG 由绿岩带的拉斑矿形成的假设，因此排除了它们与古洋壳俯冲的遗传联系。最可接受的模型似乎是卡累利阿省TTGs的形成，这是受羽流影响下地壳镁铁矿熔融的结果。太古宙TTGs与显生宙斜花岗岩明显不同，不仅在地块的形状和大小上，而且在许多地球化学特征上，特别是较低的HREE、Sc、Y和Ti含量。