Petrogenesis and Geochemical Characteristics of Carboniferous Volcanic Rocks of Chagannur Iron Deposit Area in Western Tianshan,Xinjiang
The paper studies petrology,geochemistry,Nd,Sr isotope geochemistry of Carboniferous volcanic rocks in Chagannur iron deposit located in northeastern Yili block in western Tianshan.The rocks consist of basalt(a little),andesite,trachyte,rhyolite and volcaniclastic rock.Most of them belong to high-K calc-alkaline and shoshonite series,whereas a few rocks belong to calc-alkaline and low-K tholeiitic basalt.They are enriched in LREE and LILE(Rb,Ba,Th and U) with obvious depletions of Nb,Ta and Ti,which suggest an active continental margin environment.LA-ICP-MS ziron U-Pb dating of rhyolite suggests an isotopic age of(321.2±2.3)Ma,indicating that they were created by the subduction of ocean lithosphere of north Tianshan Ocean toward south beneath the Yili block.eNd(t) values of rocks are positive and initial 87Sr/86Sr(0.704 0-0.716 3) is variable.Basaltic magma derived from depleted mantle wedge,and andesitic magma derived from root of continental arc crust near the Moho surface,and rhyolitic magma source should be located in the underpart of lower crust of the continental arc.