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

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 + Na2O) ranging from 1.26% to 6. 28%, Al2O3 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 (Sigma REE = 36. 21 x 10(-6) similar to 97. 10 x 10(-6)) and LREE enrichment ((La/Yb)(N) = 2. 88 similar to 6. 72), but weak negative Eu anomaly (Eu/Eu* =0. 74 similar to 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.