Geochemistry and zircon U-Pb geochronology of the diorite associated with the Wuling iron deposit in Western Tianshan Mountains, Xinjiang

Abstract: The Wuling diorite stock was intruded in volcaniclastic rocks of the Carboniferous Dahalajunshan Formation. Iron ore deposits were discovered in the contact zone or the interior of the stock. Zircon LA-ICP-MS U-Pb dating of the diorite yielded a weighted mean 206Pb/238U age of （307.7±0.8）Ma. Positive εNd(t) values vary from3.1 to 4.6, initial 87Sr/86Sr ratios are relatively low (0.7043-0.7046), and Nd model ages vary between 695Ma and 818Ma and fall on the mantle trend line in the 87Sr/86Sr(t) versus εNd(t) diagram. These data indicate a mantle source for the Wuling diorite. However, high Th values (1.61-3.24μg/g) and Th/Ta ratios (6.1-7.9) imply that the magma experienced a certain degree of contamination by continental crust. Therefore, the Wuling diorite magma might have been formed by the fractional crystallization of basaltic magma affected by crustal material. Although some traces of arc magmatism can be detected, the Wuling dirote was actually formed by intraplate magmatism. This diorite was emplaced when block rotation occurred between the Yili and Tarim plates after the termination of the West Tianshan accretionary orogeny. It is inferred that the generation of the magma was probably related to the detachment of an orogenic root zone or a local squeezing-stretching structural transition zone within the Yili plate.