西天山查岗诺尔铁矿区石炭纪火山岩地球化学特征及岩石成因

Petrogenesis and Geochemical Characteristics of Carboniferous Volcanic Rocks of Chagannur Iron Deposit Area in Western Tianshan,Xinjiang

对伊犁地块东北缘查岗诺尔铁矿区石炭纪火山岩进行了系统的岩石学,锆石U-Pb年代学,岩石地球化学,Nd、Sr同位素地球化学研究。该区火山岩包括玄武岩(少量)、粗面岩、安山岩、流纹岩以及火山碎屑岩,它们的化学组成绝大多数属于钾玄岩系列和高钾钙碱性系列,少数玄武岩和安山岩属于钙碱性和低钾拉斑玄武岩系列。微量元素方面,它们相对富集轻稀土元素和大离子亲石元素(Rb、Ba、Th和U),相对亏损高场强元素(Nb、Ta和Ti),具有活动大陆边缘型火山岩的亲和性。流纹岩LA-ICP-MS锆石U-Pb谐和年龄为(321.2±2.3)Ma,表明该套火山岩形成于早石炭世末期北天山大洋型岩石圈向伊犁地块之下俯冲的活动大陆边缘带。所有样品εNd(t)>0,N(87Sr)/N(86Sr)初始值变化较大(0.704 0～0.716 3)。玄武岩岩浆源区为俯冲板片之上亏损地幔楔,安山岩岩浆源区为莫霍面附近的岛弧型地壳根部,流纹岩岩浆源区则为岛弧型下部地壳。

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.εNd（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.