杭州泗岭铝质A型花岗岩的发现及其构造意义
Discovery of the Siling aluminous A-type granite in Hangzhou and its tectonic significance
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摘要: 提要：初步研究表明，以往被认为是典型的S型花岗岩或改造-重熔型花岗岩的泗岭岩体应为铝质A型花岗岩。该岩体高硅、碱、钾而明显贫钙、镁；高（K2O+Na2O）/ CaO值（平均16.79）和AKI指数（平均0.92）；FeO?鄢/MgO比值大（平均13.95），高于M型、S型和I型花岗岩，而与世界A型花岗岩平均值（13.4）相近；岩石为弱碱性、准铝-弱过铝质，富含稀土元素、HFSE元素，高Rb、F和Nb，反映其具A型花岗岩的成分特征。泗岭岩体氧同位素δ1 8O为 +8‰～+9‰，反映岩浆主要起源于下地壳。该岩体侵位于拉张的构造环境，是晚白垩世早期一次重要的构造-岩浆热事件，同时也反映了区域性孝丰—三门湾大断裂与学川—湖州大断裂在晚白垩世早期处于拉伸阶段。Abstract: Abstract：The Siling rock mass, which was formerly regarded as typical S-type granites or reworked anatectic granites, should be aluminous A-type granites. This rock mass is rich in silica, alkalis and potassium and distinctively poor in calcium and magnesium; it has high K2O+Na2O/ CaO values (average 16.79) and a high AKI index (average 0.92)；high FeO?鄢/MgO ratios (average 13.95), higher than that of M-type, S-type and I-type granites but close to the average value (13.4) of A-type granites worldwide；the rock is weakly alkaline, metaluminous-weakly peraluminous quality, rich in REE and HFSE , high in Rb, F and Nb, which are also the characteristics of A-type granites. The δ18O values of the Siling rock mass range from +8‰ to +9‰. All these suggest that the magma of the granites was mainly derived from the lower crust. The rock mass was emplaced into an extensional environment, which was an important tectono-magmato-thermal event in the early Late Cretaceous. It also indicates that the regional Xiaofeng-Sanmenwan fault and Xuechuan-Huzhou fault were in their extended stage in the early Late Cretaceous.
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Keywords:
- aluminous A-type granite /
- geochemistry /
- tectonic setting /
- late Yanshanian /
- extension /
- Siling pluton
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