首页|Early Ordovician-Middle Silurian Subduction-Closure of the Proto-Tethys Ocean:Evidence from the Qiaerlong Pluton at the Northwestern Margin of the West Kunlun Orogenic Belt,NW China
Early Ordovician-Middle Silurian Subduction-Closure of the Proto-Tethys Ocean:Evidence from the Qiaerlong Pluton at the Northwestern Margin of the West Kunlun Orogenic Belt,NW China
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Early Paleozoic magmatism in the West Kunlun Orogenic Belt(WKOB)preserves im-portant information about the tectonic evolution of the Proto-Tethys Ocean.This paper reports whole-rock compositions,zircon and apatite U-Pb dating,and zircon Hf isotopes for the Qiaerlong Pluton(QEL)at the northwestern margin of WKOB,with the aim of elucidating the petrogenesis of the pluton and shedding insights into the subduction-collision process of this oceanic slab.The QEL is mainly com-posed of Ordovician quartz monzodiorite(479±3 Ma),quartz monzonite(467-472 Ma),and syeno-granite(463±4 Ma),and is intruded by Middle Silurian peraluminous granite(429±20 Ma)and dia-base(421±4 Ma).Zircon εHf(t)values reveal that quartz monzodiorites(+2.1 to +9.9)and quartz mon-zonites(+0.6 to +6.8)were derived from a mixed source of juvenile crust and older lower crust,and sye-nogranites(-5.6 to +4.5)and peraluminous granites(-2.9 to +2.0)were generated from a mixed source of lower crust and upper crust;diabases had zircon εHf(t)values ranging from-0.3 to +4.1,and con-tained 463±5 Ma captured zircon and 1048±39 Ma inherited zircon,indicating they originated from enriched lithospheric mantle and were contaminated by crustal materials.The Ordovician granitoids are enriched in LILEs and light rare-earth elements,and depleted in HFSEs with negative Nb,Ta,P,and Ti anomalies,suggesting that they formed in a subduction environment.Middle Silurian peralumi-nous granites have the characteristics of leucogranites with high SiO2 contents(74.92 wt.%-75.88 wt.%)and distinctly negative Eu anomalies(δEu = 0.03-0.14),indicating that they belong to highly fractionated granite and were formed in a post-collision extension setting.Comparative analysis of these results with other Early Paleozoic magmas reveals that the Proto-Tethys ocean closed before the Middle Silurian and its southward subduction resulted in the formation of QEL.
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