Tectonic Setting and Provenance of Sandstones from Triassic Daheba Formation in the West Qinling Orogenic Belt
The Daheba formation is the latest strata exposed in the Xiahe-Luqu area of the West Qinling Oro-genic Belt(WQOB),with recording the Indosinian regression event.In this study,based on the stratigraphic se-quence characteristics,major and trace element compositions and zircon U-Pb dating of the sandstone,we traced the origin of the sandstone and explored the tectonic settings of the Daheba Formation.The Daheba Formation consists of feldspar sandstone,lithic feldspar sandstone,conglomerate clastic feldspar sandstone.The SiO2 con-tent of sandstone range from 64.11％to 68.72％with an average of 65.45％.The sandstones are also character-ized by high Al2O3(13.61％～15.19％),lower Fe2O3(0.82％～1.72％),CaO(2.393％～3.32％)and MgO(0.06％～0.1％)contents.They have high rare earth elements(REE)range from 184.13×10-6 to 434.06× 10 6,and show negative Eu anomaly in the chondrite normalized diagram.They also have similar Th,Zr,Ti,and Co,Ni compositions with that of active continental margin sediments.The detrital zircon U-Pb ages from the sand-stones are mainly concentrated in 253.3～448.7 Ma,1 536～2 067 Ma and 2 204～2 520 Ma,and show five age peaks at 278.2 Ma,448.5 Ma,1 757.6 Ma,1 986.4 Ma and 2 445 Ma,with the youngest ages at 253.3 Ma.These indicates that the Daheba Formation was deposited in an active continental margin setting,and the detritus origi-nated from the upper crust igneous rocks.The main sources for the detritus is possibly of the basement of the northern Qinling,the eastern part of the Qilian,and the southern edge of the North China Plate in the northern parts of the study area with small parts from the magmatic rocks and polycyclic sediments in the West Qinling.
Daheba formationdetrital zircontectonic settingprovenanceWest Qinling Orogenic Belt
万方数据
维普
