Zircon U-Pb geochronology and geochemistry of the Tagelake monzogranites in South Tianshan block: Constraints on crustal magmatic origin and tectonic setting

This paper is the result of geological survey engineering.

Objective The Tagelake strip pluton, outcropped at the south Tianshan terrane in Southwestern Tianshan orogenic belt, is composed of monzogranites. Determining the formation mechanism of the monzogranites has important implications for the crust-derived magma origin and the time limit of subduction and ocean basin closure in South Tianshan Mountains.

Methods In order to determine the formation mechanism of the monzogranites, detailed zircon U-Pb geochronology, major elements and trace elements were firstly conducted.

Results LA-ICP-MS zircon geochronology study reveals that the monzogranites in the Tagelake area crystallized at (284.0±1.9)-(284.3±3.2) Ma, indicative of an Early Permian pluton. The results of major elements and trace elements reveal that the monzogranites display the characteristics of A-type granite: (1) The contents of SiO₂ (70.92%-72.78%), K₂O+Na₂O (7.91%-8.44%) and A/CNK (0.89-0.99) are high, indicating that monzogranites are metaluminous rock and belongs to the high potassium calcium alkaline series; (2) The monzogranites are enriched in LREE (196×10^-6-280×10^-6) and depleted in HREE (22.8×10^-6-28.2×10^-6). Negative Eu anomaly is obvious, with δEu values of 0.51-0.64, and the monzogranites are characterized by fractionated chondrite-normalized REE patterns; (3) The monzogranites are enriched in Rb, Th, K and other large ion lithophile elements and depleted in Nb, Ta, Zr, P, and other high field strength elements.

Conclusions Combined with the regional tectonic evolution, it is considered that the Tagelake monzogranites were formed in the post-collision tectonic setting.