新疆吾尔喀什尔地区晚泥盆世铁列克提组火山岩LAICP-MS锆石U-Pb年龄、地球化学特征及构造意义

LA ICP-MS zircon age,geochemistry and tectonic setting of the volcanic rocks from the Late Devonian Tieliketi Formation in the Ur Kashgar Mountain,western Junggar

西准噶尔晚泥盆世铁列克提组主要分布于吾尔喀什尔山西部，为一套海陆交互相火山-沉积地层。火山岩地球化学研究表明，Si02含量为51．18％～62．48％，Ti02为O．60％～1．49％、全碱（K20＋N赴O）为1．26％～6．28％，相对富钠贫钾。A120，为15．53％～18．68％、MgO为2．64％～7．55％，Mg^#为41．2-58．5，属于亚碱性系列。稀土元素总量高（∑REE=36．21×10^-6-97．10×10^-6），轻、重稀土分馏较强（（La／Yb）。=2．88-6．72），具轻微负Eu异常（Eu／Eu^#=0．74～1．07）。相对富集LILE（Rb、Ba、Th和K），亏损HFSE（Zr、Hf），Nb和Ta强烈亏损，Ti轻微亏损。岩石源区主要受俯冲流体交代，受地壳物质混染较弱，整体具有弧火山岩的地球化学特征。与火山岩伴生的凝灰岩LAICP-MS锆石u-Pb同位素测年结果为363．3±4Ma。综合分析认为铁列克提组火山岩属于大陆边缘弧火山作用的产物，同时，博什库尔．成吉斯岩浆弧可能至少延续至晚泥盆世。这为进一步认识西准噶尔博什库尔一成吉斯岩浆弧的性质及构造演化提供了证据。

The Late Devonian Tielieketi Formation, overall a suit of continental-marine alternating facies volcanic-sedimentary rocks, is mainly distributed in the west of Ur Kashgar Mountain, western Junggar. The volcanic rocks are belong to sub-alkaline series, with SiO2 ranging from 51.18% to 62. 48%, TiO2 ranging from 0. 60% to 1.49% , total alkaline （K2O＋ Na.20） ranging from 1.26% to 6. 28%, A1203 ranging from 15.53% to 18. 68%, MgO ranging from 2. 64% to 7. 55%, and Mg^#ranging from 41.2 to 58.5, and also showing relative rich in sodium, but poor in potassium. Moreover, all samples are characterized by higher rare earth elements （∑REE =36. 21 × 10^-6 -97. 10 × 10^-6） and LREE enrichment （（La/Yb） N =2. 88 -6. 72） , but weak negative Eu anomaly （Eu/ Eu^＊ =0. 74- 1.07）. In addition, they display LILE enrichment （such as Rb, Ba, Th and K）, HFSE depletion （Zr and Hf）, obvious Nb and Ta negative anomalies, and slight Ti depletion. The results show geochemical characteristics of arc volcanic rocks as a whole, suggest that all the rocks from the Tielieketi Formation were derived from continental marginal arc setting with the source mainly affected by the fluid from the subduction zone, and weak crustal material contamination. The U-Pb zircon LA ICP-MS age of the tuff closely associated volcanic rocks is 363.3 ± 4.0Ma. These observations, in combination with previous work, indicate that the Boshchekul-Chingiz arc may sustain to the Late Devonian at least, furthermore, provides evidence for further understanding the property and tectonic evolution of the Boshchekul-Chingiz arc in the western Junggar.