黑龙江黄松群的地球化学特征及形成环境分析

Geochemical characteristics of Huangsong Group in Heilongjiang and its tectonic environments

对佳木斯—兴凯地块西南缘的黄松群进行其物源区特点、古风化条件和构造背景等分析结果显示,该套变质碎屑岩源岩为泥砂质沉积岩,源区母岩以中酸性火成岩为主。风化作用相关指数CIA、CIW及PIA,由杨木组到阎王殿组逐渐增高,而ICV值则呈递减趋势,体现了风化作用由弱到强,成分成熟度逐渐升高的特点。主量元素特征值SiO_2=69.95%、TiO_2=0.58%、TFe_2O_3+MgO=5.34%、Al_2O_3/SiO_2=0.21,微量元素特征值La=37.54×10^(-6)、Ce=72.83×10^(-6)、δEu=0.60、ΣREE=182.29×10^(-6)。REE配分模式与活动大陆边缘碎屑沉积物类似,并且在不同构造环境判别图解中,绝大多数样品投影点落入活动大陆边缘区。地球化学特征表明,黄松群碎屑岩可能沉积于活动大陆边缘环境。

The provenance characters, weathering conditions and tectonic setting of Huangsong Group in southwestern margin of Jiamusi-Khanka massifs in eastern Heilongjiang were discussed. The results show that the source rocks of metamophic rocks are dominated by argillaceous sandstone and arenaceous mudstone, and the parent rocks are mainly intermediate-acid igneous rocks. The chemical index of alteration (C IA ), chemical index of weathering (CIW) and plagioclase index of alteration (PIA) show an obvious increasing from the Yangmu Formation to the Yanwangdian Formation, while the index of compositional variabitlity (ICV) is decreased, which reflects the weathering was getting strong and the compositional maturity was increasing gradually from Yangmu Formation to Yanwangdian Formation. The contents and ratios of some major elements ( Si02 = 69. 95% , Ti02 = 0. 58% ,TFe20 3 + MgO = 5. 34% and Al20 3/S i0 2 = 0. 21 ) and trace elements ( La = 37. 54 X 10 ~6 , Ce = 72. 83 X 10 ~6 ,^Eu =0. 60 and XREE = 182. 29 X 10 6 ) , and the REE distribution patterns, are similar to those of clastic rocks deposited in the active continental margin. This is supported by ploting of the geochemical values of samples in different tectonic discrimination diagrams. All these indicate that the Huangsong Group was deposited in the active continental margin.