Mineral chemistry, geochemistry and U-Pb SHRIMP zircon data of the Yangxin monzonitic intrusive in the foreland of the Dabie orogen  

作　　者：XUE Huaimin DONG Shuwen JIAN Ping 

机构地区：[1]Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China Chinese Academy of Geological Sciences, Beijing 100037, China Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

出　　处：《Science China Earth Sciences》2006年第7期684-695,共12页中国科学（地球科学英文版）

基　　金：supported by the Chinese Ministry of Science and Technology(Grant Nos.2003CB716502 and TG1999075505);the National Natural Science Foundation of China(Grant No.40472035).

摘　　要：The Yangxin composite intrusive consists of three generations of plutons, among which 90% are the second generation intrusions. The second generation intrusion has U-Pb SHRIMP zircon age of 134±2 Ma, substantially younger than the early stage of the Yanshanian. Amphibole and biotite, major mafic minerals in the Yangxin plutons, are rich in magnesium, suggesting a deep source of their parental magma, possibly derived from the upper mantle. Whole rock geochemical data on these rocks show that they have high Al2O3 (15.92%―16.38%), relatively high alkali (Na2O+K2O = 6.95%―7.37%) and higher Na2O contents than K2O (Na2O/K2O = 1.47―1.94). They also have high Sr con-tents (816―897 μg/g) are enriched in strong incompatible elements such as Rb, U, Th, K and LREE, but depleted in HREE and Y. Strong fractionation of LREE from HREE as indicated by high (La/Yb)N ratios ranging from 17.83 to 20.86. Although with little difference, the whole characteristics of the Yangxin intrusive body are greatly similar to the adakite, referring that the formation of the parental magma may relate with the partial melting of the basalt underplating from the mantle after delamina-tion of the mountain root of the Dabie orogen. The body has been uplifted about 5 km since cooling concretion, the average rate was only about 0.04 mm/a,much slower than that of the Dabie orogen in late Mesozoic, but the rates of denudation in two area are similar in Cenozoic.The Yangxin composite intrusive consists of three generations of plutons,among which 90% are the second generation intrusions. The second generation intrusion has U-PbSHRIMP zircon age of 134±2 Ma, substantially younger than the early stage of the Yanshanian.Amphibole and biotite, major mafic minerals in the Yangxin plutons, are rich in magnesium,suggesting a deep source of their parental magma, possibly derived from the upper mantle. Whole rockgeochemical data on these rocks show that they have high Al_2O_3 (15.92%—16.38%), relatively highalkali (Na_2O+K_2O = 6.95%-7.37%) and higher Na_2O contents than K_2O (Na_2O/K_2O = 1.47-1.94). Theyalso have high Sr contents (816-897 μg/g) are enriched in strong incompatible elements such as Rb,U, Th, K and LREE, but depleted in HREE and Y. Strong fractionation of LREE from HREE as indicatedby high (La/Yb)_N ratios ranging from 17.83 to 20.86. Although with little difference, the wholecharacteristics of the Yangxin intrusive body are greatly similar to the adakite, referring that theformation of the parental magma may relate with the partial melting of the basalt underplating fromthe mantle after delamina-tion of the mountain root of the Dabie orogen. The body has been upliftedabout 5 km since cooling concretion, the average rate was only about 0.04 mm/a, much slower thanthat of the Dabie orogen in late Mesozoic, but the rates of denudation in two area are similar inCenozoic.

关 键 词：zircon  SHRIMP  Yangxin intrusive  foreland  DABIE orogen. 

分 类 号：N[自然科学总论]