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Mineralogical and Element Geochemical Characteristics of the Late Triassic-Middle Jurassic Sedimentary Rocks in Southwestern Fujian Province: Constraints on Changes of Basin Tectonic Settings
详细信息   
摘要
The Wenbinshan Formation, Lishan Formation and Zhangping Formation in Upper Triassic-Middle Jurassic in southwestern Fujian experienced a large-scale transgressive-regressive event. The geochemical characteristics which is showed by the major element analysis and ICP-MS trace element and rare earth element analysis show that the source rocks of the set of sediments are mainly sedimentary rock and granite (Rb > 100 × 10-6; K2O > 1%; Hf = 5. 38 × 10-6 ～ 14. 17 × 10-6; La/Th =1. 64 ～4. 94). The source rocks of the Wenbinshan Formation and Lishan Formation sediments are from the sedimentary rock and granite of the passive continental margin source area and acidic arc source area (Rb > 300 × 10-6; K2O > 2%; Hf = 3. 75 × 10-6 ～ 6. 64 × 10-6; La/Th = 2. 73 ～ 4. 21). The source rocks of Zhangping Formation are from the granite in the acidic arc source area and the mixture source area of felsic and mafic. The studies of the compositions of the sandstone framework have shown that Wenbinshan Formation source material are mainly from the volcanic arc orogen; Lishan Formation and Zhangping Formation are from the volcanic arc orogen and the magmatic arc source area. It is consistent with the source area showed by the mudstone geochemistry. The association of the lithology and facies in different ages,the geochemistry characteristics of the mudstone and the mineral composition of the sandstone and the locations of the samples in Zr-Th,La-Th-Sc,Th-Co-Zr /10 tectonic setting discrimination diagrams have showed that Wenbinshan Formation sediments deposited on the back-arc extensional basin with the characteristics of both a passive continental margin and a continental island arc (∑REE =22. 51 ×10-6 ～ 152. 6 × 10-6; LREE/HREE =7. 21 ～15. 01,δEu =0. 69 ～0. 90; La/Yb =5. 64 ～16. 93; (La/Yb)N = 3. 66 ～ 10. 99). Lishan Formation sediments deposited on the active continental margin which is near the continental island arc (∑REE =140. 4 ×10-6 ～ 335. 5 × 10-6,LREE/HREE=9. 52～15. 90,δEu =0. 48 ～0. 62,La/Yb =11. 04 ～21. 13; (La/Yb)N = 7. 17 ～ 13. 72). It is also the back-arc basin squeeze with the characteristics of a passive continental margin (∑REE = 115. 4 × 10-6 ～ 383. 4 × 10-6,LREE/HREE = 8. 30 ～ 20. 27,δEu = 0. 55 ～ 0. 67,La/Yb = 8. 42 ～ 30. 12; (La/Yb)N = 5. 47 ～ 19. 56). Zhangping Formation sediments deposited on the back-arc basin squeeze with the characteristics of an active continental margin (∑REE = 98. 34 × 10-6 ～ 260. 5 × 10-6,LREE/HREE = 11. 28 ～ 19. 38,δEu = 0. 56 ～ 0. 64,La/Yb = 10. 19 ～ 23. 91; (La/Yb)N = 6. 62 ～ 15. 52) which is near the continental island arc.

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