The connection of volcanic-plutonic rocks of the Daqinggou complex pluton in the central Qilian belt,NW China
Investigating the genetic relationship between intrusive and volcanic rocks in large silicic magma systems can provide insights in revealing magma dynamics processes and the compositional evolution of continental crust.The Daqinggou intrusive-volcanic complex from the Yanchiwan area in the central Qilian belt provides a best opportunity for the genesis of intrusive rocks and volcanic rocks.This paper focuses on the Daqinggou volcanic rocks and related intrusive rocks.Field geology,geochemical,zircon U-Pb dating,zircon Hf isotope combined with zircon trace element analysis indicate the formation ages of rhyolite,monzogranite and granodiorite in the Daqinggou volcanic-intrusive complex were 456±2 Ma,454±3 Ma and 455±4 Ma,respectively.These intrusive and volcanic rocks share similar zircon Hf isotopic composition with the εHf(t)value ranging from-5.2 to 0.3.Geochemical analyses indicate that the Daqinggou intrusive-volcanic complex is enriched in Si and K,and it exhibits enrichment in LILE sand depletion in HFSE as well as pronounced Eu-negative anomalies.Integrated analyses suggest these three types of intrusive-volcanic rocks are derived from the same magma reservoir and formed by continuous crystal-melt crystal fractionation in the magma chamber.The rhyolite is the product of the activation and fractionation of pre-existing crystal mush,while the monzogranite is the intrusive fractioned magmas without eruption and the granodiorite represents the product of crystal mush with low degree of fractionation.
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