LA-ICP-MS U-Pb zircon geochronology, geochemistry and kinetics of the Wenquan ore-bearing granites from West Qinling, China

摘要

Many hydrothermal Cu-Mo-Au deposits related to granitoid intrusives were recentiy discovered in the West Qinling Orogenic Belt (WQOB). These deposits were mainly formed during the late Indosinian epoch (ca. 214 Ma), and the regional geological setting of Cu-Mo ore formation in WQOB during this epoch is poorly understood until now. This paper describes the geochronology and geochemistry of the Wenquan ore-bearing pluton, a composite granite body, to study the geologic background of magmatic emplacement and ore formation. The Mo mineralisation occurs at the contact between a fine-grained biotite monzogranite and a medium- to fine-grained porphyritic monzogranite. Zircon ~(206)Pb/~(238)U ages of 223 ±3 Ma (biotite monzogranite) and 225 ± 3 Ma (porphyritic monzogranite) were obtained. Geochemical analyses show that the Wenquan pluton is a high-K calc-alkaline to shoshonite series rock with relatively high LREE and low HREE and a moderate to weak negative Eu anomaly. Relatively negative anomalies of Ba, Ti, P, Nb, Ta also exist. These results imply that the Wenquan pluton was emplaced during a transitional process (from collision to extension) between the Yangtze Craton and North China Craton. During the later Indosinian epoch, the East Qinling Orogenic Belt (EQOB) and WQOB had similar tectonic settings, and intensive magmatic activity and Mo mineralisation occurred. The EQOB was then involved in the Mesozoic subduction of the Pacific plate, and its subsequent tectonic evolution was different from that of the WQOB.