首页|Zircon U-Pb geochronologic,geochemical and Sr-Nd-Pb isotope characteristics of the Beidaban granites in the North Qilian Orogenic Belt:Petrogenesis and tectonic implications
Zircon U-Pb geochronologic,geochemical and Sr-Nd-Pb isotope characteristics of the Beidaban granites in the North Qilian Orogenic Belt:Petrogenesis and tectonic implications
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Zircon U-Pb geochronologic,geochemical and Sr-Nd-Pb isotope characteristics of the Beidaban granites in the North Qilian Orogenic Belt:Petrogenesis and tectonic implications
The tectonic evolution and crustal accretion pro-cess of the North Qilian Orogenic Belt(NQOB)are still under debate because of a lack of integrated constraints,especially the identification of the tectonic transition from arc to initial collision.Here we present results from zir-con U-Pb geochronology,whole-rock geochemistry,and Sr-Nd-Pb isotope geochemistry of the Beidaban granites to provide crucial information for geodynamic evolution of NQOB.Zircon U-Pb dating yields an age of 468±10 Ma for the Beidaban granites and most of the Beidaban samples contain amphibole,are potassium-rich,and have A/CNK values ranging from 0.7 to 0.9,illustrating that the Middle Ordovician Beidaban granites are K-rich,metaluminous,calc-alkaline granitoid.The geochemical characteristics indicate that the Beidaban granites are transitional I/S-type granitoids that formed in an arc setting.The isotopic com-positions of initial(87Sr/86Sr)i values ranging from 0.70545 to 0.71082(0.70842 on average)and eNd(t)values ranging from-10.9 to-6.7(-8.8 on average)with two-stage Nd model ages(TDM2)of 1.74-2.08 Ga suggest that the Bei-daban granites originated from Paleoproterozoic crustal materials.In addition,the initial Pb isotopic compositions(206Pb/204Pb=19.14-20.26;207Pb/204Pb=15.71-15.77;208Pb/204Pb=37.70-38.26)and geochemical features,such as high Th/Ta(17.43-30.12)and Rb/Nb(6.01-15.49)values,suggest that the Beidaban granite magma source involved recycled crustal components with igneous rocks.Based on these results in combination with previously pub-lished geochronological and geochemical data from other early Paleozoic igneous rocks,we suggest that the timing of the tectonic transition from arc to the initial collision to the final closure of the North Qilian Ocean can be constrained to the Middle-Late Ordovician(ca.468-450 Ma).
GranitoidsZircon U-Pb datingSr-Nd-Pb-isotopesPetrogenesisNorth Qilian Orogenic Belt
Tao Yang、Zhi-yuan Sun、Ming-liang Wang、Xiao-qiang Zhu、Jing-yu Zhao
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The First Institute of Geology and Mineral Exploration,Gansu Provincial Bureau of Geology and Mineral Exploration,Tianshui 741020,China
School of Resources and Civil Engineering,Suzhou University,Suzhou 234000,China
School of Geography and Tourism.Anhui Normal University,Wuhu 241000,China
Granitoids Zircon U-Pb dating Sr-Nd-Pb-isotopes Petrogenesis North Qilian Orogenic Belt
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