华北克拉通北缘尚义地区新太古代TTG成因分析:洋壳玄武岩不同深度下熔融的产物

尚义玄武岩为尚义-赤城新太古代洋壳残片的组成端元,地球化学性质指示其源于富集地幔。根据稀土元素分配特征,尚义玄武岩可被分为TH1型(稀土元素平坦型)和TH2型(稀土元素分异型)。尚义TTG属于中钾偏铝质钙碱性岩类,其Al2O3含量与低铝型TTG相近,同时微量元素Rb、Sr、Y和REE表现出俯冲板片熔融成因的埃达克岩的性质。根据主量元素SiO2、K2O、Na2O、Al2O3和微量元素Rb、Sr、Y、REE等指标判别和微量元素平衡熔融模式计算得出,尚义TTG形成压力遍及低压—高压范围,是洋壳玄武岩(TH1型)在深度压力变化的条件下部分熔融形成的,其中的低铝型TTG形成于低压熔融。

The genesis of Neoarchean TTG in the Shangyi area of the northern margin of North China Craton: melt from basalt of oceanic crust at varying depth

Shangyi basalt is a component part of Neoarchean oceanic crust in Shangyi-Chicheng fault zone, and its geochemical characteristics suggest an enriched mantle source. The basalt can be divided into two types: TH1 (Flat-REE) and TH2(Fractionated-REE). Shangyi TTG is mainly of the medium-potassium, metaluminous and calc-alkaline type, and similar to low-Al2O3 TTG owing to its low Al2O3 content. In addition, Shangyi TTG shows features of adakite by slab melting according to trace elements Rb, Sr, Y and REE. Based on features of major and trace elements (SiO2, K2O, Na2O, Al2O3, Rb, Sr, Y, REE) and trace element equilibrium melting calculation, the authors have reached the conclusion that Shangyi TTG was formed throughout the low-high pressure range and was probably produced from partial melting of oceanic crust basalts (TH1 type) at varying depth, with the low-Al2O3 type formed under low pressure.