Geochronological and geochemical characteristics of the Caledonian Longquan pluton in southern Zhejiang, and their geological significance

Abstract

The Longquan pluton is a rare Caledonian granitic rock mass in southern Zhejiang. Studies on the Longquan pluton using petrology, geochemistry, and chronology were conducted in this paper, which reveal that it is composed of granite-monzogranite assemblage (granitoid) and tonalite-trondhjemite-granodiorite assemblage (TTG). The two types of rocks are generally enriched in large ion lithophile elements Rb, Ba, Th, U and K, and depleted in high field strength elements Nb, Ta, P and Ti, showing the characteristics of island arc magmatic rocks. The geochemical characteristics of the TTG rocks show that they belong to the typical high-pressure type TTG, and its magma originated from the remelting of the basic lower crust under the action of subducted slab fluid. While the granitoids were mainly derived from partial melting of ancient crustal sediments. Neither of them was significantly contaminated by mantle. The zircon SHRIMP U-Pb and LA-ICP-MS U-Pb dating results show that the Longquan pluton was formed between 443±3 Ma~410±3 Ma. Combined with its petrological and geochemical characteristics, it is indicated that the subduction of oceanic crust had still existed in the Longquan area until early Devonian.

Keywords

• ttg
• zircon u-pb age
• caledonian
• longquan pluton