论文
WANG Feng, XU Wen-Liang, LI Jun, PEI Fu-Ping, CAO Hua-Hua-
Global Geology.
2009, 28(4):
403-413.
Gabbro-diorite zircons from Yantongshan in central Jilin Province are euhedral-subeuhedral in shape, and display homogeneous growth zoning and high Th /U ratios (0.63~1.49) , suggesting theirmagmatic origin. LA-ICP-MS zircons U-Pb dating indicate that 206 Pb /238U ages of 24 spots ranging (118 ±1) to (125 ±1) Ma with a weighted mean age of (122 ±1) Ma (MSWD = 4.5) , implying the crystallization of this rock body as Early Cretaceous in age. The contents of SiO2 are 52.41% ~53.38% , TiO2 1.27% ~1.95% , MgO 3.34% ~ 4.27% (Mg# = 44~47) , TFe2O3 8.42%~9.48% , Na2O 3.99%~4.31% , K2O 1.54%~1.97%, Na2O /K2O 2.05~2.75 and Al2O3 16.87% ~19.60%, characterizing high Na and Al. The gabbro-diorites have high light rare earth elements (LREEs) , low heavy rare earth elements (HREEs) and weakly positive Eu anomalies in chondrite- normalized rare earth element curves, and with high L ILEs (Rb, Ba and Th) and relative low HFSEs (Nb, Ta, Zr, Hf and Ti) in p rimitive mantle-normalized trace element spider diagram. The primary magma of gabbro-diorite in Yantongshan derived from the partialmelting ofmantle wedge which metasomatized by subduction fluids, and formed under an extensional environment similar to back-arc basin during the subduction of the Paleo-Pacific Plate.