Journal Article
Geochemistry, petrogenesis and geological significance of Early Carboniferous adakite in Sawuer region, West Junggar, Xinjiang
Li, H; Li, YJ; Xu, XY; Yang, GX; Wang, ZP; Xu, Q; Ning, WT
The Aketamu Formation, as a new defined lithostratigraphic unit in Sawuer region, West Junggar, is composed of intermediate volcanic lavas and pyroclastic rocks, with minor of acidic volcanic lavas. The LA-ICP-MS zircon U-Pb age of rhyolite from the Aketamu Formation is 337. 9 +/- 0. 77Ma. Therefore, the rhyolite is formed in Early Carboniferous. Geochemically, the andesites in the Aketamu Formation are characterized by high SiO2 (53. 42%similar to 64. 74%), Al2O3 (16. 05%similar to 19. 23%) and Na2O (4. 05% similar to 8. 13%), and low K2O (0. 36%similar to 3. 65%). They have high Sr (448. 1 x 10(-6)similar to 1507 x 10(-6)) contents, high Sr/Y (36.6 similar to 89. 0) ratios, and slightly positive Eu anomalies. Moreover, the andesites are enriched in large-ion-lithophile elements (such as K, Rb, Ba, Th and U) and light rare earth elements, and are depleted in high-field-strength elements (such as Nb, Ta and Ti) and heavy rare earth element, especially Y and Yb, showing the characters of a typical adakite. The studied results show that the andesites from Aketamu Formation were the products resulting from slab melting, with the residual minerals (eg. amphibole + garnet) in the source of garnet amphibolite. In combination with the regional geological background, the authors hold that the subducted oceanic slab edges were heated by the asthenospheric mantle rise through slab window, which is the result of the southward subduction of the Irtysh-Zaysan Ocean between Kazakhstan in the south and Altai in the north. The reaction of upward migrating adakitic magmas with mantle peridotite gave rise to the adakite and Nb-enriched arc basalt suites, and led to the Cu-Au mineralization at the same time. The discovery of Early Carboniferous adakite in Aketamu Formation provides evidence for further understanding of the Late Paleozoic tectonic evolution, magmatism and metallogenic of ore deposits in West Junggar.
Physical Sciences - Other Topics; Adakite, Early Carboniferous, Aketamu Formation, Sawuer region, West; Junggar; asian orogenic belt, phanerozoic crustal growth, nb-enriched basalt,; u-pb geochronology, island-arc magma, sr-nd isotopes, continental-crust,; tectonic implications, eastern tianshan, north xinjiang