Abstract:

Abstract:  The granite of Jiaoziding dome core is located in backLongmenshan Area of the northwest margin of Yangtze Block. The study of granites zircon SHRIMP UPb geochronology and geochemistry is aiming at constraining its formation age and petrogenesis. The results show that the zircons of the samples in deformative granite and massive granite of the Jiaoziding granites have internal oscillatory zoning; zircons of the Jiaoziding granites have higher Th/U ratios（0.521.23， 0.321.16）and are igneous in origin. The results of zircon SHRIMP UPb dating for deformative granite and massive granite were （793±11） Ma and （792±11） Ma respectively，which indicates that the granite intrusions formed in Nanhua period of the late Neoproterozoic，and their formation times are fully coincident. The Jiaoziding granite is high in SiO2 （72.01％77.65％）and Al2O3（12.12％14.18％），and its A/CNK=0.951.13（1.04 on average）. It is a typical peraluminous granites，with supersaturation in Al and Si，and is identified as Stype granite. The abundance of ∑REE varies in the range of (75.8179.97)×10-6（77.89×10-6 on average）. The rocks show a LREE enrichment pattern and obviously weak to intermediate negative Eu anomalies. The trace element geochemistry is characterized evidently by negative anomaly of Ta，Nb，Ti，etc. and positive anomaly of Rb，Ba，Sr，etc. The granite emplaced by underplating of granitic magma，which formed through partial melting of sedimentary mainly of arenite，and is typical crust source petrogenesis. The Jiaoziding granite shows the characteristics of postcollisional granite, and is regarded as the postorogenic granite. Thus the granite intrusions are interpreted as syncollisional granites resulted from the crustal thickening caused by active continental margin subduction and arccontinent collision orogeny during the Neoproterozoic in the northwest margin of Yangtze Block. The granitic intrusion formed in a transitional environment from syncollision (compressional environment) to postcollision （extensional environment），and is the product of the initial breakup of Rodinia supercontinent.

Key words:

Key words: peraluminous granites; geochemistry; zircon SHRIMP UPb age; Neoproterozoic; northwest margin of Yangtze Block; Rodinia supercontinent