Volcanic Deposits of the Carboniferous Coal -bearing Series in Western Shandong Province

The study area situtates in western Shandong including Xinwen, Feicheng, Yanzhou, Tengxian, Zibuo coal fields ect. This paper mainly deals with Carboniferous strata for the study of volcanic deposits. According to petrlolgical and mineralogical determination by means of polarizing microscope. X - ray diffraction, infrared absorption, spectrum and chemerical analysis ect., composition, texture, sedimentary structures and distribution of pyroclastic rocks of the Carboniferous coal measure in the area are reached. The pyroclastics belong to itermediate - acidic basicity and consist principally the crystalline materials of quartz, plagiocase, sanidine and biotite etc., intermediate and glassy rock fragments and a little of shards. The content matrix is high. The diagenetic mineralogical alteration of pyroclastics is intense, they may be chloritiza-tion, clayization, calcitization or devitritilation of volcarnic glass etc. The results of chemical analysis about the primary composition are consistent with that of petrologic analysis. Ti, P. Cr, Ga, V, Sr, Zr in pyroclastic rocks are higher ban that in normal sedimentation. Compared with the means of trace elemets in the Crust, Na, V, Mn, Cr, Ni, Co and Fe is very low and Zr, K. La and Ce is very high in pyroclastic rocks. Additionally, the ratio between TiO₂ and Al₂O₃ is low, it is found that pyroclastic meterials are intermediate -acidic basicity and tend to be alkaline and come from the crust. Pyroclastic rock is rich in the LREE, poor in the HREE and have a distinct negative anomalty of Eu, shows the original protolith types of pyroclastic materials are neutral extrusive -rock related to continental-crust - deriver alkaline femic rock, indicaing that the volcanic eruption originated from the rift valley with the continental plates. According to the mentioned data the serwater encroachment of the Middle Carboniferous Benxi stage in the Linyi area is earlier than in other areas of southrn North China. There are differences in sedimentary assemblage of the Upper Carboniferous between south and north divided by Xinwen and Feicheng, and the Upper Permian coal - bearing series on the south of Fengxian and Peixian is south type and northern facies. All of that are directly controlled by tectonic movements at that time and the resuited volcanic action. Therefore, the sedimentary type of the Carboniferous is a coal -bearing sediment of volanic - sedimentary facies association. The finds of similar pyroclastics in other areas of North China also show that the crustal movemet of the Carboniferous in North China is not stable and there are large tectonic movements and freguent volcanic actions. There are a few layers of volcanogenic tonsteins in the coal measure which are steadly and widely occrued over the area. For example, The coal seam No. 11 in Xinwen, No. 15 and No. 16 in Laiwu, No. 7 in Feicheng and No. 15 in Linyi, Jining and Tengxian correspond to each other.