大别山北缘石炭系碎屑岩地球化学及碎屑锆石年代学分析及其对物源区大地构造属性判别的制约

大别山北缘石炭系作为古生代唯一不变质或轻微变质的沉积地层,记录了其物源信息和古生代的构造演化.针对研究区这一地质特征,本文分析了研究区砂岩的碎屑组分、常量元素、微量元素和稀土元素,以及碎屑锆石的同位素年龄,并据此对物源区的大地构造属性进行了研究.研究区碎屑岩主要以中细粒石英砂岩和长石石英砂岩为主,砂岩的QFL平均值为Q 76.2％,F 15.9％,L7.9％,Q/(F+ L) 4.26;主要元素氧化物平均百分含量SiO263.69％,Al2O3 11.25％,MgO 3.66％,CaO 5.15％,Fe2O3T 6.15％,K2O 1.68％,Na2O 0.68％;部分特征微量元素Th,U,Hf,Sc,Zr,Y平均含量分别为10.78×10-6、2.64×10-6、4.39×10-6、15.67×10-6、166×10-6、25.33×10-6.Rb/Sr,Th/U,La/Y,La/Sc,Th/Sc比值分别为1.49、4.10、14.75、31.92和0.89;稀土元素总量ΣREE平均146.2×10-6(54.11×10-6 ～256.0×10-6),Eu异常0.64,轻稀土略有富集,La/Yb为12.58(3.94～15.42),(La/Yb)N为9.02.锆石年龄测定表明,早石炭世地层中碎屑锆石的年龄主要集中在400 ～500Ma,晚石炭世地层中碎屑锆石年龄主要为900～ 1300Ma,其次为2000～ 2800Ma.上述结果表明大别山北缘石炭系沉积物来源于不同的源区,包括早古生代的大陆岛弧、扬子板块中-新元古代基底以及华北板块古-中元古代基底.

Geochemistry and detrial zircon geochronology of Carboniferous detrital rocks in the northern margin of Dabie Mountains, central China and constraints to distinguishing the provenance tectonic attribute

The Carboniferous is a suite of un-metamorphosed or slightly metamorphosed sedimentary strata in the northern margin of the Dabie Mountains,and it recorded the information of the provenance and the Paleozoic tectonic evolution. The authors analyze the compositions of major,trace and rare elements,the detrital compositions of sandstone and the dating of detrital zircons in the study area,and investigate the tectonic attribute and evolution of the provenance. Medium-fine grain quartz sandstone and feldspar-quartz sandstone are the major in the study area. The QFL averages of sandstones are Q 76. 2% ,F 15. 9% ,L 7. 9% and Q / ( F + L) 4. 26; the major element oxide averages of Carboniferous sandstones are SiO 2 63. 69% ,Al 2 O 3 11. 25% ,MgO 3. 66% ,CaO 5. 15% ,Fe 2 O T 3 6. 15% ,K 2 O 1. 68% and Na 2 O 0. 68% ; the part characteristic trace elements like Th,U,Hf,Sc,Zr,Y have averages of 10. 78 × 10 - 6 ,2. 64 ×10 - 6 ,4. 39 ×10 - 6 ,15. 67 ×10 - 6 ,166 ×10 - 6 and 25. 33 × 10 - 6 ,respectively; and the ratios of Rb/Sr,Th/U,La/Y, La / Sc and Th / Sc are respectively 1. 49,4. 10,14. 75,31. 92 and 0. 89; the average of ΣREE is 146. 2 × 10 - 6 ( 54. 11 ×10 - 6 ～ 256. 0 × 10 - 6 ) ,δEu is 0. 64,light REE enrichment. La/Yb is 12. 58( 3. 94 ～ 15. 42) ,and ( La/Yb) N is 9. 02. The dating of detrital zircons shows that the major U-Pb age of zircons in Early Carboniferous are about 400 ～ 500Ma,while in Late Carboniferous the ages of zircons are mostly 900 ～ 1300Ma and secondly 2000 ～ 2800Ma. These reveal that the Carboniferous sediment derived from different provenance,including the Early Paleozoic island-arc system,Middle-Late Proterozoic basement of Yangtze Craton,Early-Middle Proterozoic basement of North China.