Origin of the late Carboniferous Karamaili Granite Belt in Eastern Junggar, Northwest China: Zircon U-Pb and trace element constraints.

Wang, Qiwei; Zhang, Bowen; Ding, Jiangang; Zhan, Xinzhong; Yalikun, Yaxiaer; Aishan, Mayila; Wei, Xiang; Wang, Yacong; Peng, Haowei; Sun, Yafei; Sun, Yunlong

The variability of magmatic zircon geochemical signatures can reecord different tectonic settings and be used to accurately determine regional tectonic evolution. For example, Th/U values of magmatic zircons correlate with tectonic stress regimes (continental extension and compression) and the magmatic environment. Previously, the Karamaili Granite Belt (KGB) has been considered to be a product of siliceous magmatic activity in the late Palaeozoic post-collisional extensional environment of the Eastern Junggar, and consensus is that it is composed of A2-type granite. In this study, the U-Pb zircon geochronology of the KGB indicates it crystallized between 320 and 310 Ma. The Th/U ratios of the 494 magmatic zircons range from 0.22 to 1.22 but in the southeastern part of the KGB exhibit high Th/U ratios (maximum 1.22) and high coefficients of variation (maximum 45.2%), compared to the smooth Th/U variation (mostly <0.8) and low coefficients of variation (minimum 13.5%) in the northwestern part. The δEu values of zircons in the KGB range from 0.1 to 1.16, with less variability (mostly <0.2), but show an increasing trend in the extensional area (maximum 1.16). Zircon trace element signatures indicate that the most KGB granites exhibits highly differentiated I-type granite characteristics. In addition, tin mineralization in the KGB is primarily controlled by a tectonic environment of compression and is closely associated with highly differentiated I-type granites. This is distinctly different from granites with mafic microgranular enclaves (MMEs), such as those in the Sabei and Huangyangshan plutons, which formed in an extensional environment with significant crustal growth. Hence, the Th/U and δEu indicators of zircons suggests the KGB was formed during a tectonic transformation of overall compression and local extension at the end of plate subduction, and a local extensional environment was formed at the Junggar Ocean end of the subduction in this area, which introduced large-scale mantle-derived material of mantle origin, and that crustal vertical growth was strong, forming a thicker juvenile crust.

GEOLOGICAL time scales; ZIRCON; GRANITE; SUBDUCTION; TIN

International Geology Review, 2025, Vol 67, Issue 2, p166

0020-6814

Academic Journal

10.1080/00206814.2024.2376324