关键词: 秦岭梁岩体, LAICPMS, 锆石UPb同位素年龄, 秦岭造山带

Abstract: Triassic granite are widespread in the Qinling orogenic belt, which directly records the important information of the evolution process of the Qinling orogenic belt. The Qinlingliang intrusion is located in the north of the ShangDan suture belt, mainly consisting of the quartz monzonite porphyry, with the Kfeldspar as phenocryst (some phenocrysts have a white rim of plagioclase) and mainly quartz (25%), plagioclase (45%), Kfeldspar (10%), biotite (15%) and amphibole (5%) as matrix. The zircons in the Qinlingliang intrusion show the characteristics of magmatic zircon with fine euhedral crystal and zonation. The LAICPMS zircon UPb ages of two samples are (2165±21) Ma and (2194±26) Ma, indicating that the Qinlingliang intruded in the Late Triassic. The age is consistent with the time of the northern subduction of the MianLüe oceanic crust(248-200 Ma), indicating that they have close relationship. The geochemical characteristics of the Qinlingliang quartz monzonite prophyry intrusion suggest that it was the production of the arc magmatic activity under the oceanic crust subduction setting. Comprehensive discussions make it clear that the closing time of the MianLüe ocean and the beginning time of fullscale collision between Yangtze and North China plates should be later than (216-219) Ma.

Key words: Qinlingliang intrusion, LAICPMS, zircon UPb isotopic dating, Qinling orogenic belt