摘要
甘肃北山大石山岩体主要由角闪花岗岩和二长花岗岩组成,岩石的化学成分特点为过铝质(Al_2O_3含量为 12.18%～13.37%)、富硅(SiO_2含量为74.22%～78.38%)、偏碱(Na_2O+K_2O 为7.60%～8.50%),FeO^T/MgO 值高,CaO 和 MgO 含量低(分别为0.01%～0.99%和0.05%～1.15%),富含 Y、Nb 等高场强元素(HFSE)以及 F、Sr、 Ba 和 REE(∑REE=102.3×10^(-6)～120.02×10^(-6))低。这些特点与本区的 I 型和 S 型花岗岩有明显差别,是一种典型的 A_2型花岗岩。大石山岩体 Rb-Sr 等时线年龄为273 Ma,表明北山地区在海西晚期即进入造山后拉张裂解环境。
The Dashishan intrusive in Beishan area of Gansu Province mainly consists of biotite potassiumfeldspar granites. The granites of Dashishan are metaluminous （Al2O3 = 12.18% - 13.37% ） and are characterized by high SiO2 （74.22 % -78.38 % ）, Na2O ＋ K2O（7.60 % -8.50 % ）, FeO^T/MgO ratio, REE（ 102.3×10^-6-120.02×10^-6）, Y, Nb and F, and low CaO（0.01% -0.99% ）, MgO（0.05% - 1.15% ）, Sr and Ba. These characteristics are very different from characteristics of I-type and S-type granites in Beishan area, but quite similar to A2 type granites. The Dashishan intrusive has a Rb-Sr isochron age of 273 Ma. It is therefore suggested that crustal rifting might have started in late Hercynian in that area.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2006年第2期90-96,共7页
Acta Petrologica et Mineralogica
基金
中国地质调查局区域地质调查项目(200213000020)
关键词
A型花岗岩
地球化学特征
北山地区
大石山
A-type granite
geochemical characteristics
Beishan area
Dashishan
