五台山晚太古代花岗岩的成因及其动力学意义

五台山晚太古代花岗岩（～2.540 Ga），主要由花岗闪长岩、二长花岗岩、少量的英云闪长岩、奥长花岗岩组成，全岩化学分析表明它们具有中～高钾钙碱性花岗质岩浆性质，LILE富集和高的 w(Rb)/w(Sr) (即: Rb/Sr)比值，相对较低的 w(Sr)/w(Y)、w(La)_n/w(Yb)_n、w(Nb)/w(Ta) 和 w(Zr)/w(Hf) 比值，右斜式稀土配分模式，Nb、Ta、Ti亏损，但是它们均表现了Nd T_DM＝2.54～2.72 Ga和明显的正ε_Nd(t)值。这些地球化学特征表明其钙碱性花岗质岩浆形成于晚太古代大洋岛弧环境，来源于弧下玄武质初生地壳的部分熔融，并经历了一定程度的结晶分异。由于晚太古代洋壳向大洋岛弧俯冲、脱水，引起上覆地幔楔的部分熔融形成弧下初生地壳玄武质物质，这些弧下玄武质物质在少于37km环境下部分熔融形成五台山晚太古代钙碱性花岗质岩浆。

Petrogenesis of Neoarchean Wutaishan Granitoids and Its Geodynamic Significances

Neoarchean Wutaishan granitoids (～2.540 Ga) are mainly consisted of granodiorite, monzogranite, a little tonalite, trondhjemite. The geochemistry in whole rocks indicates that they have the characters of middle to high potassium calc-alkaline granitic magma. They exhibit the LILE enrichments and higher w(Rb)/w(Sr) ratios (Rb/Sr), relatively lower w(Sr)/w(Y) and w(La)_n/w(Yb)_n ratios, w(Nb)/w(Ta) and w(Zr)/w(Hf) ratios are similar to Chondrite, right inclined REE patterns, and Nb, Ta, Ti depletion, but all of them have the neodymium T_DM＝2.54～2.72 Ga and the evidently positive ε_Nd(t) values. These important geochemical features indicate that the calc-alkaline granitic magma formed in the Neoarchean oceanic island arc tectonic environment, derived from the partial melting of the juvenile original basaltic crust, and underwent some crystallization fractionation. The Neoarchean oceanic crust subducted to the oceanic island arc and dehydrated, caused the partial melting of the overlain mantle wedge, formed the underplating basaltic rocks underlain the island arc. These basaltic rocks were partially melted in the environment of less 37km crustal depth and formed the Neoarchean Wutaishan calc-alkaline granitic magma.