新疆西天山铁木里克铁矿床火山岩锆石U-Pb年代学、岩石地球化学特征及地质意义

Zircon U-Pb age,Hf isotopic and geochemistry of volcanic rocks from Tiemulike iron deposit in western Tianshan,Xinjiang,and their geological significance

铁木里克铁矿位于西天山阿吾拉勒铁铜成矿带中段,矿床围岩为一套以粗面安山岩、安山岩和流纹岩为主的连续变化的中酸性火山岩。本文通过对铁木里克铁矿床火山岩进行LA-ICP-MS锆石U-Pb定年,并且结合Hf同位素和岩石地球化学研究,对火山岩的形成时代以及大地构造背景进行探讨。锆石LA-ICP-MS测年结果显示,粗面安山岩、安山岩以及流纹岩的测年结果分别是318.8±2.3Ma、320.8±2.5Ma和319.1±3.5Ma。地球化学分析表明该套火山岩属于高钾钙碱性-钾玄岩系列,富集轻稀土元素(LREE)和大离子亲石元素(LILE;如Rb、Th、K),重稀土元素(HREE)配分平坦,同时具有Nb、Ta的强烈亏损,具有明显的岛弧火山岩地球化学特征。在火山岩的大地构造判别图解上,样品点都落在了大陆弧部分。锆石的Hf同位素显示εHf(t)具有一致的变化范围(+6.2^+12.0),指示火山岩具有相同的岩浆来源,都是来源于早古生代新生陆壳的重熔,形成于相同的构造岩浆背景下。结合区域地质资料,本文认为铁木里克铁矿床出露的这套高钾钙碱性-钾玄岩系列火山岩可能是南天山洋闭合末期到陆陆碰撞早期大陆弧岩浆作用的产物。

The Tiemulike iron deposit is located in the middle segment of Awulale iron-copper metallogenic belt of which the host rock is a series of middle to acid rocks containing andesite,trachyandesite and rhyolite. In this paper,representative samples of volcanic rocks from the Tiemulike iron deposit were analyzed for major,trace element and zircon U-Pb,Lu-Hf dating to validate their tectonic setting and formation ages. LA-ICP-MS analysis shows that the zircon U-Pb age of andesite,trachyandesite and rhyolite are318. 8 ± 2. 3Ma,320. 8 ± 2. 5Ma and 319. 1 ± 3. 5Ma. Geochemical data indicates that the most of the volcanic rocks range in composition from high-K calc-alkaline to shoshonitic,with light rare earth element（ LREE） and large ion lithosphere element（ LILE;e. g.,Rb,Th,K） enrichment and almost flat heavy rare earth element（ HREE） patterns as well as strongly negative Nb,Ta; similar to features of arc volcanic rocks. In the plots of tectonic discrimination,the volcanic rocks are mainly projected in arc setting regions.εHf（ t） of zircon Lu-Hf isotopic analysis data shows a consistent range（ ＋ 6. 2 ~ ＋ 12. 0）,indicates that the whole rocks may be derived from the same parent magma and formed in the same tectonic settings. Combined with the regional geological data,we therefore suggest that the high-K calc-alkaline to shoshonitic volcanic rocks were probably the products of continental island-arc magmatism during the late stage subduction to continental collision.