辽宁丹东黄旗地区辽河群变质岩地球化学特征及成因探讨

GEOCHEMISTRY AND GENESIS OF THE METAMORPHIC ROCKS OF LIAOHE GROUP IN HUANGQI AREA, LIAONING PROVINCE

黄旗地区处于中朝准地台东部、胶辽台隆之营口-宽甸台拱南东端.研究区为辽东早前寒武纪地质构造分区东部,主要出露中生代岩浆杂岩和古元古代岩浆岩及地层,古元古代辽河群广泛发育.主要变质岩类型可划分为：片岩、变粒岩、浅粒岩、长石石英岩、钙硅酸岩及大理岩.研究区辽河群变质岩岩石化学特征为：1）硅酸盐类岩石SiO2平均含量为47.32%～78.6%,总体K2O〉Na2O;2）碳酸盐类岩石总体CaO〉MgO,总的特征是富钙、镁.辽河群各类变质岩微量元素含量相似度较高,F、Rb含量高,浓度克拉克值较大.辽河群变质岩的稀土元素特征为：ΣREE平均值为205.9×10^-6,LREE/HREE平均值为12.8,δEu平均值为0.56;稀土分布图谱属右缓倾斜型,轻稀土分异较重稀土分异好,属于轻稀土富集型,具负铕和弱负铈异常.结合区域内辽河群原岩建造特点,可推断在古元古代时期研究区属地槽型大地构造环境,反映了辽河群地层整体上构成了一个较完整的火山-沉积建造序列.

Huangqi area is tectonically located in the southeastern end of Yingkou-Kuandian anteclise of Jiao-Liao platform uprise in the east of Sino-Korean paraplatform. The study area belongs to the east of Early Precambrian tectonic division of Eastern Liaoning, where Mesozoic magmatic complex and Paleoproterozoic magmatite and strata occur and Paleoproterozoic Liaohe Group is widely developed. Metamorphic rocks are mainly schist, granulite, leucoleptite, arkose quartzite,calcsilicate rock and marble. The petrochemical characteristics of the metamorphic rocks are as follows： 1）The average content of SiO2 in silicate rocks is 47.32%- 78.6%, generally K2O〉Na2O; 2）Carbonate rocks are generally rich in Ca and Mg, with CaO〉MgO. The metamorphic rocks in Liaohe Group take very similar trace element content, high content of F and Rb and relatively high Clarke values of concentration. The REE average ΣREE of the metamorphic rocks is 205.9×10^-6, with average LREE/HREE of 12.8 and δEu of 0.56. The REE distribution pattern is gently gradient to the right, with better differentiation of LREE than that of HREE, enrichment in LREEs and negative Eu and slightly negative Ce anomalies.Combining with the characteristics of protolith formation of Liaohe Group regionally, it is concluded that the study area was a geosyncline tectonic setting in Paleoproterozoic Era, reflecting that Liaohe Group strata formed a complete volcanicsedimentary formation series on the whole.