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
About author: Wang Dongan, male, was born in 1937. Now he is a professor of the Institute of Geology, Chinese Academy of Sciences, and engages in sedimentology.
Cite this article:
. GEOCHEMICAL FEATURES OF THE ORDOVICIAN SILICEOUSROCKS IN THE MIDDLE PART OF EAST KUNLUNAND RECOGNITION OF THEIR SEDIMENTARYTECTONIC ENVIRONMENTS[J]. JOURNAL OF PALAEOGEOGRAPHY, 1999, 1(1): 41-53.
. 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.
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