大兴安岭北段泥盆纪大民山组硅质岩地球化学特征及沉积环境

GEOCHEMISTRY AND SEDIMENTARY ENVIRONMENT OF THE SILICEOUS ROCKS FROM DEVONIAN DAMINSHAN FORMATION IN NORTHERN DAXINGANLING

大兴安岭北段泥盆纪大民山组硅质岩与硅质泥岩共生出现，硅质泥岩中产丰富海相化石．硅质岩Al／（Al＋Fe＋Mn）值在0．60-0．71之间，平均值0．65．在Al-Fe—Mn三角图上，样品均落入非热水成因区．MnO／TiO2比值在0．07～0．34，平均值为0．18．m值在13．87～47．15之间，平均值为23．90．CaO／（Fe＋CaO）值在0．65—0．98之间，平均值为0．78．∑REE较低，平均62．77×10^6,LREE／HREE平均值为6．67，相对富集轻稀土，具有轻度的Ce正异常（δCe1．08—1．30，平均值1．16）．结合硅质岩沉积环境判别图解，一致表明大民山组硅质岩形成于离大陆较近的大陆坡或边缘海的高盐度海水环境．

The silicalite and siliceous mudstone of Devonian Daminshan Formation are developed in northern Daxinganling, where the siliceous mudstone is rich in marine fossils. The Al/（Al＋Fe＋Mn） values of the siliceous rocks range from 0.60 to 0.71, with an average of 0.65. In the Al-Fe-Mn ternary diagram, all samples fall into non-hydrothermal siliceous rock area. The MnO/TiO2 ratio is 0.07 - 0.34, and 0.18 in average. The m value is 13.87 to 47.15, averagely 23.90. The CaO/ （Fe＋CaO） value is between 0.65 and 0.98, with an average of 0.78. The ∑REE is low （averagely 62.77×10^6） and the average LREE/HREE is 6.67. The siliceous rocks are relatively enriched in LREEs, with slightly positive Ce anomalies （SCe 1.08 - 1.30, averagely 1.16）. Combined with the sedimentary environment discrimination diagram for siliceous rocks, it is indicated that the siliceous rocks of Daminshan Formation are formed in the continental slope close to continent or the high-salinity seawater of marginal sea.