Radiolarian Chert and Island-Arc Volcanic Rocks in Xiapugou Tibet: Records of Neo-Tethys Intra-Oceanic Subduction System?
XU Rong-ke
ZHENG You-ye
FENG Qing-lai
SHAN Liang
WEI Jun-hao
ZHANG Xiang
ZHANG Gang-yang
MA Guo-tao
PANG Ying-chun
Abstract：The stratigraphic units composed of radiolarian chert and lava were found in Xiapugou in western of Yarlung Zangbo Suture Zone during the 1/250 000 field geology survey. The radiolarian cherts are characterized by SO_2 ranging from 89. 47 to 92. 94%, Si/Al ratio ranging from 43 to 67, Al/( Al+Fe+Mn) ratio from 0. 68 to 0. 74, The average MnO/TiO_2, , Ce/Ce~* and LaN/CeN ratio is 0. 60, 0. 89 and 1. 09, which indicates the radiolarian chert was formed in transitional environment between continental margin basin and the oceanic basin, and had much more close relationship with the former one. The lava mainly belongs to andesite and is characterized by (1) low TiQ_2 varying from 0. 75 to 0. 98%; (2) gentle enrichment in LREE;, (3) fluid-soluble elements, such as Ba, U and Pb, are extremely enriched compared with LREE; (4) depleted in high-field strength elements (HFSE) such as Nb, Ta, Ti). All these characters imply that the stratigraphic units are consistent with a juvenile intra-oceanic arc, which maybe represents the remains of New-Tethys intra-oceanic subduction system The early Cretaceous fauna of radiolarian fossils from the chert including Alievium cf. regulare, Alievium cf. fatuum, Archaeospongoprurtum cf. patricki, Archaeodictyimitra mitra Dumitrica et aL have been identified,yielding a upper time restrain of this juvenile intra-oceanic arc.
Keywords：Cretaceousradiolarianchertlithologyisland arcXiapugouYarlung Zangbo Suture Zone.
Publication Date：2009-01-01
Pages：11( 884-894 )