Geochemistry, Geochronology, and Hf Isotopic Compositions of the Tuanyushan Pluton from the Western Segment of the Northern Qaidam
详细信息
- 责任者：Zhu Xiaohui (Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits ; MLR ; Xi’an Center of Geological Survey ; CGS ; Xi’an 710054 ; China) ; Chen Danling
- 刊名：Geological Journal of China Universities
- 出版年：2013
- 卷期：19(2)
- 关键词：花岗闪长岩 ; granodiorites ; 柴达木盆地 ; Qaidam Basin
- 页码：p.233-244
- 图表：illus., 4 tables, 70 refs.
- 分类号：0801
- issnNo：ISSN1006-7493
- isbnNo：CN32-1440/P
摘要
Granodiorites from the western segment of the Northern Qaidam have relatively high contents of SiO 2(66.35%~70.04%),alkali(Na 2 O+K 2 O=7.20%~7.57%) and Na(Na 2 O/K 2 O=2.37~3.38),but low magnesium indexes(Mg # =23~26) and A/CNK(1.00~1.02),suggesting that these rocks belong to calc-alkaline and weakly peraluminous granites.Moreover,these rocks have high contents of Sr(858×10-6 ~1020×10-6) and low contents of Y(4.65×10-6 ~6.31×10-6),Yb(0.38×10-6 ~0.54×10-6),showing characteristics of high Sr/Y ratios(162~192).U-Pb isotopic compositions of zircons yield an intrusion age of(437.4±3)Ma.Combined with the ultra-high pressure(UHP) metamorphic ages of 423~458 Ma in the Northern Qaidam,this pluton should have resulted from partial melting of thickened mafic lower crust during deep subduction of continental crust under conditions ofP>1.2 GPa andT>800 ℃with residual mineral assemblages of garnet+amphibole in source rocks.Lu-Hf isotopic compositions display large variations with ε Hf(t) changing from-11.4 to 8.15,and two-stage model ages can be divided into two groups.One group ranges from 888 to 1078 Ma(positive ε Hf(t) values) and the other from 1300 to 1699 Ma(negative ε Hf(t) values).Moreover,two points at the cores of zircon crystals have t DM2 c =2.45 Ga and 3.00 Ga(the associated U-Pb ages are >2.4 Ga),respectively.These results suggest that the Tuanyushan pluton was likely derived from complicated sources which mainly consist of Meso-Neoproterozoic and Paleoproterozoic crust.The results also imply that the earliest crust in the Northern Qaidam may be formed in Archean.