摘要
Late Silurian-early Devonian mafic--intermediate dykes occur in the Xiemisitai mountain of the northern West Junggar. However, their ages, petrogenesis and geodynamic process remain to be unraveled. We report firstly in situ zircon U–Pb and hornblende 40Ar-39Ar ages, geochemical and in situ zircon Hf isotopic data for the Xiemisitai dykes. The Xiemisitai dykes give zircon U–Pb ages of 416.7±2.1 Ma and 405.1±2.5 Ma and hornblende 40Ar-39Ar age of 405.9±4.9 Ma, respectively. They are characterized by high εHf(t)values(+11.9 to +15.5), suggesting a depleted mantle features. The Xiemisitai dykes show low Mg#(46–59) and low Cr(11.3–197 ppm) and Ni(19.9–102 ppm) abundances indicating that they have experienced significant fractional crystallization. These dykes contain hornblende and biotite and display negative Nb-Ta-Ti anomalies, enrichment of LREEs, LILEs and depletion of HREEs and HFSEs with high Ba/La ratios, similar with an origin from a depleted lithospheric mantle metasomatized by subducted slabderived fluids. In addition, the Xiemisitai dykes are plotted within melting trends with little to no garnet(Cpx:Grt=6:1) in their source. The La/Yb vs. Tb/Yb plot also indicates the presence of less than 1% residual garnet in the source region for the Xiemisitai dykes. Therefore, it can be inferred that the Xiemisitai dykes were generated at a correspondingly shallow depth, mostly within the spinel stability field. Finally, the Xiemisitai dykes were most probably generated by partial melting of metasomatized lithospheric mantle in relatively shallow level(<80 km). They could be possibly triggered by the asthenospheric upwelling as a result of the rollback of the subducted Irtysh-Zaysan oceanic lithosphere.
基金
supported by the National Key R&D 445 Program of China(2017YFC0601206)
the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(XDB18020203)
the Opening Foundation of State Key Laboratory of Continental Dynamics,Northwest University(17LCD04)
National Science Foundation of China(Grant nos.41473053,41573045,41611530698,41873060 and 41830216)
作者简介
first anthor and the corresponding author:YIN Jiyuan,male,born in 1983 in Guiyang City,Guizhou Province,doctor,professor of Institute of Geology,Chinese Academy of Geological Sciences.He is now interested in the study on petrogeochemistry and isotope geochemistry of granites and dyke,and Low temperature-thermochronology.Email:yinjiyuan1983@163.com,Mobile phone:+8618211032203.
