Stratiform tuffaceous siliceous rocks are widely exposed in the Nomhon－Xiangride area of the middle part of East Kunlun, mostly occur within volcanic lava and above itThe siliceous rocks are compact,well bedded, and are of unique geochemical featuresThey contain little organic matterTheir SiO2 content is relatively low, mostly ranging from 77% to 87%, while Al2O3, Na2O and K2O contents are relatively highMoreover, Na2O content is higher than that of K2O. w(MnO)/w(TiO2) is much higher than 0.5, and the average of N(Al)/N(Al+Fe+Mn) ranges from 0.6 to 0.82The trace element characteristics of the siliceous rocks are obviously different from those of the siliceous rocks formed in stable sedimentary areas of the platform typeThe abundance of the trace elements is positively proportional to that of the co existing volcanic lava evidently, with obviously high contents of Rb, Zr, Hf, Ga, Th, Au and low contents of organismrelated and hydrothermalwaterrelated elements, such as Ba, V, Cr, Cu, Rb, U, etc The average content of REE is 833 μg/g, and LREE/∑REE value generally ranges from 0.91 to 0.98, showing relative enrichment of LREE ChondriteREE normalized patterns demonstrate“V”shape with clear Eu anomaly and very scarce Ce anomaly δ30Si falls into the range from 0‰ to －0.4‰ Initial 87Sr / 86Sr value is 0.714 1on the average, close to that of tuffiteA series of correlation charts also indicate that the siliceous rocks have the same provenace with the coexisting volcanic lavaVarious diagrams suggest that they are formed in volcanic island arc belts or active continental margins
. GEOCHEMICAL FEATURES OF THE ORDOVICIAN SILICEOUSROCKS IN THE MIDDLE PART OF EAST KUNLUNAND RECOGNITION OF THEIR SEDIMENTARYTECTONIC ENVIRONMENTS[J]. JOPC, 1999, 1(1): 41-53.
1Sugisaki R,Kimoshita T Major elements chemistry of the sediments on the central Pacific transect Wake to Tahiti, GH80-1 Cruise In: Mixumo A ed. Geol Survey Japan Cruise Report, 1982, 18:793～312
2Sugisaki R Relaton between chemical composition and sedimentation rate of Pacific ocean\|floor sediments deposited since the middle Cretaceous:Basic evidence for chemical contraints on depositional environments of ancient sediments JGeol1984，92:235～259
3王东安扬子地台晚古生代以来硅岩的地球化学及其成因地质科学，1994，29(1)：41～54
4Bostrom K The origin and fate of ferromanganese active ridge sediments,Stokholm Contrib Geol， 1973,27:147～243
5Adachi M, Yamamoto K, Suglsaki R Hydrothermal chert and associated rocks from the Northern Pacific: their geological significance as indication of oceanic ridge activitySedimentary Geology, 1986，47(1/2):125～148
6王东安，陈瑞君扬子地台不同时代层状硅岩的硅同位素结果的讨论沉积学报，1996，14(2)：82～88
7Bostrom K,Kracmer T,Gartner S Provenance and accumulation rates of opaline silica Al, Ti, Fe, Mn, Cu, Ni, and Co in Pacific pelagic sediment Chemical Geology,1973，11(1/2):123～148
8Yamamoto K Geochemical characteristics and depositienal environment of cherts and associated rocks in the Franciscan and Shimento terranes Sedimentary Geology, 1987，52(1/2):65～108
9陈瑞君，王东安宣化烟筒山含铁建造中硅岩的地球化学特征见:叶连俊主编生物有机质成矿作用北京：海洋出版社，1996 145～153
10Bostrom K Genesis of ferromanganese deposits-diagnostic criteria for recent and old depositsIn:Rona P A,Bostrom K,Laubier L，Smith K L, Jr., eds Hydrothermal processes at seafloor spreading centers, Plenum Press,1983. 473～489
11Bostrom K，Rydell H Geochemical behavior of U and Th during exhalative sedimentary process,In: Bostrom K, et al, eds. N289°-La Genese Des Noducles De Manganese, Colloques Internationaux du CNRS,1986151～161
12Steinberg M,Bonnot-Courtois G, Tlig SGeochemical contribution to the understanding of bedded chertIn:Iijima A, Hein J R, Siever R, eds. Siliceous Deposits in the Pacific Region Elsevier, Amsterdam1983193～210
13Murray R W,Jones D L，Buchholtz ten Brink M R Diagenetic formation of bedded chert inferred from rare earth, major, and trace element chemistry of Franciscan complex,Monterey Group and DSDP cores. Eos, 1990, 71:1392
14Shimizu H,Masuda A Cerium in chert as an indication of marine environment of its formationNature，1977，266:346～348
