Abstract:

The Qimantag in East Kunlun orogen has strong magmatic activity from the Silurian to Devonian, and its formation is related to oceanic lithosphere subduction orogeny and collision-post-collision orogeny. In this paper, zircon U-Pb chronology and whole-rock major and trace element geochemistry are carried out on the Hua-tugou granodiorite in Qimantag, and the petrogenesis and tectonic background are discussed. LA-ICP-MS zircon U-Pb dating of the granodiorite is (396.5±4.6) Ma, which is the product of Early-Middle Devonian magmatic activity. The whole-rock SiO₂ content is 63.01%-74.70%, showing characteristics of high K₂O (1.53%-4.01%), Na₂O (2.16%-3.80%) and Al₂O₃ (12.95%-14.48%), Mg^# is 17.01-61.23, belonging to calc-alkaline and high-K calc-alkaline series. The chondrite-normalized REE patterns are moderately right-dipping and smooth, with negative Eu anomaly (δEu=0.48-0.72). Trace element spider diagram shows that the rocks are enriched in large ion lithophile elements (LILEs), such as Rb, Th, La, Ce and light rare earth elements (LREEs), and is depleted in Nb and Ta, Ba and other high field strength elements (HFSEs), belonging to I-type granite. Combined with the magmatic age, geochemical characteristics and regional tectonic evolution, we considered that the granodiorite is the partial melting product of orogenic crustal materials (especially accretionary crustal materials), mixing with some mantle-derived material, and experienced fractionation of feldspar and other minerals during the magma evolution. The tectonic regime may have been a compression-extension transition from syn-collisional to post-collisional setting.

Key words: I-type granite, high-K calc-alkaline, Devonian, East Kunlun orogen, Qimantag