Geochemistry Characteristics of Lata Ordovician Intrusive Rock from Kekenaike Area in Tuokexun Xinjiang,and Its Geological Significance
Kekenaike area is located in the eastern part of the Kekenaike continental margin island arc of Ear-ly Paleozoic,The Late Ordovician gneiss granodiorite and gneiss granitic were discover.The tectonic environment of Kekenaike intrusive rock is discussed through field observation、LA-ICP-MS zircon U-Pb age and geochemical testing,which provides a basis for further study of subduction convergence in the North Tianshan Ocean.The age results show that the granitic gneiss is 448.0±2.4 Ma,which belong to late Ordovician.Geochemical characteristics:the granodiorite gneiss's average value of SiO2 is 64.69％,MgO is 1.18％,Al2O3 is 14.85％and CaO is 2.78％,(Na2O+K2O)is 6.47％,K2O/Na2O is 1.06％,the Rittman index(σ)is 1.88,A/CNK is 1.07.;The granitic gneiss's average value of SiO2 is 70.08％,MgO is 0.54％,Al2O3 is 13.47％,and CaO is 2.00％,(Na2O+K2O)is 7.02％,K2O/Na2O is 1.45％,the Rittman in-dex(σ)is 1.80,A/CNK is 1.05.The granite is rich in Si and Mg、low in Ca.The rock is high content of(Na2O+K2O)and high content of K2O/Na2O,belongs to the high potasssium calc-alkali and metaluminous rock series,I、S-type granite.The total amount of REE is high(∑REE=290.92～436.00 × 10-6),LREE/HREE is 3.41～6.39,LaN/YbN=8.52～21.22,to-gerther with light rare earth,and weak negative Eu anomaly(δEu is 0.50～0.96).The Large ion lithophilic elements(Rb,K,Ba,Th,La,Ce)are relatively enriched,The high field strength elements(Ta,Nb,Ti)are deficit,which reveals that magma origin is closely related with convergence subduction,the characteristics of trace elements show that the magma source is characteristics of crust-mantle mixing.The geochemical characteristics of the continental marginal arc granites show that the gneiss granodiorites and gneiss granites in the Kekeanake area are the products of the North Tianshan Ocean subduction and convergence in the Late Ordovician.
NETL
NSTL
万方数据
