摘要
北京西山晚侏罗世髫髻山组粗安岩具有高的SiO2 (>5 6 % )、Al2 O3(16 .33%～ 17.9% )、Na2 O(3.11%～ 4 .80 % )、Na2 O +K2 O (6 .11%～ 8.10 % )和CaO (3.6 8%～ 5 .82 % )含量及低的MgO(<3.0 % ,Mg# ≤ 0 .5 0 )含量 ,高Sr(5 5 4× 10 - 6～ 12 5 8× 10 - 6)、低Yb(<1.70× 10 - 6)和Y(<2 1× 10 - 6) ,高Sr/Y、Y/Yb和Na2 O/K2 O(0 .93～ 2 .73)比值及低Rb/Sr比值 ;轻重稀土元素分馏十分明显 ,没有Eu异常 ,具有adakitic岩的一般特征。认为这些粗安岩起源于下地壳钙碱性玄武质岩石的部分熔融 ,与底侵作用有关。根据地球化学特征推测 ,粗安岩浆起源深度不超过 5 0km。
Late Jurassic trachyandesites from Tiaojishan Formation in Western Hills of Beijing are similar to adakitic rocks in geochemical characteristics. They contain high SiO 2(>56%), Al 2O 3(16.33%～17.9%), Na 2O(3.11%～4.8%), Na 2O+K 2O(6.11%～8.10%), K 2O(1.64%～3.59%) and CaO(3.68%～ 5.82%), low MgO(<3.0%, Mg #≤0.50), high Sr (554×10 -6 ～1?258×10 -6 ), low Yb(<1.70×10 -6 ) and low Y(<21×10 -6 ), and have high Sr/Y, Y/Yb and Na 2O/K 2O ratios and low Rb/Sr ratios. In addition, they are characterized by strongly fractionated REE and absence of Eu anomaly. It is thought that the trachyan_desites are derived from partial melting of lower_crust calc_alkaline basaltic rock and are related to the underplating of basic magma. Based on the geochemical features, the depth of magma is less than 50 km.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2001年第3期247-254,共8页
Acta Petrologica et Mineralogica
基金
国家自然科学基金资助项目 (4 9733110 )
国家杰出青年科学基金资助项目 (4 972 5 30 9)
关键词
粗安岩
下地壳钙碱性玄武质岩石
部分熔融
底侵作用
晚侏罗世
北京
成因
trachyandesite
lower_crust calc_alkaline basaltic rock
partial melting
underplating
Late Jurassic
Western Hills of Beijing
