Geochronology And Geochemistry Of Uraniferous Volcanicrocks In Tuoli Region Of The West Junggar

The Northern Xinjiang contains several significant Paleozoic volcanic belts, and has a great prospecting potential for volcanic type uranium deposits. Many uranium deposits, occurrence, mineralization and other clues of uranium mineralization have been discovered in the Late Paleozoic volcanic belts. Zhayier volcanic belt is one of important uranium belts in Western Junggar, whereas the studies on geochronology and geochemistry of volcanic rocks in the Zhayier volcanic belt are limited. Therefore, we focuses on the petrology, geochemistry and geochronology of volcanic rocks from the Beijinqi and Taergen areas in the Zhayier volcanic belt, and discusses their magma source, petrogenesis and geodynamic significance.Based on the zircon LA-ICP-MS U-Pb dating, the three volcanic rocks in the Zhayier volcanic belt occurred at 312.6 ± 4.1Ma, 299.4 ± 4.2Ma and 299.4 ± 2.6Ma, respectively, indicating that these volcanic rocks were probably formed in the Late Carboniferous. Combined with detailed field investigation and these geochronological data, we suggest that the Molaoba Formation and Qialebayi Formation belong to the Late Carboniferous, and Kujiertai formation belongs to the Early Permian.Integrating the petrology and geochemistry characteristics of the volcanic rocks in the Zhayier volcanic belt, they are mainly composed of rhyolite, dacite, and andesite, which are calc-alkaline and high-K calc-alkaline series. Geochemically, these volcanic rocks exhibit strong enrichment in light rare earth elements(LREE) and depletion in heavy rare earth elements(HREE). Of these, the rhyolite rocks show pronounced negative Eu anomalies, depletion in high field strength elements(HFSE) such as Nb and Ta, and enrichment in large ion lithophile elements(LILE) such as Rb, Ba, Th, U and K, especially in U. The rhyolite and dacite rocks are relatively depleted in Sr, P, and Ti, while the andesite rocks are slightly depleted in P.Based on the Sr-Nd isotopic analyses, the(87Sr/86Sr)i and(143Nd/144Nd)i values of the volcanic rocks in the Zhayier volcanic belt, are ranging from 0.70092 to 0.70561, and from 0.512467 to 0.512646, respectively, with the εNd(t) values between 4.3 and 7.8. Combined with geochemical features of these rocks, we thus suggest that the continental volcanic rocks in the Zhayier volcanic belt were most likely derived from the remnants of oceanic crust or arc magma source, and formed in the post-collision setting.Key words: West Junggar; Volcanic rock; Late Paleozoic; U-Pb geochronology;...