Precise age determination of mafic and felsic intrusive rocks from the Permian Emeishan large igneous province (SW China)

摘要

Radiogenic isotopic dating using different (mainly micro-beam analyses) techniques of rocks from the Emeishan large igneous province (ELIP) has yielded a range of ages from the Capitanian to the Early Triassic. In contrast, estimates based on paleontological and paleomagnetic data suggest the ELIP was emplaced rapidly (≤. 2. Ma) and that volcanism ended by ~. 257. Ma. New zircon CA-TIMS U-Pb ages, that have superior precision compared to ages from micro-beam analyses, were obtained from strategic intrusive rocks of the Panxi region (Inner Zone) of the ELIP. The Huangcao (258.9. ±. 0.7. Ma), Daheishan (259.1. ±. 0.5. Ma), Woshui (259.6. ±. 0.5. Ma) and Cida (258.4. ±. 0.6. Ma) syenitic and granitic plutons and three mafic dykes (259.2. ±. 0.4. Ma; 259.5. ±. 0.8. Ma, 257.6. ±. 0.5. Ma) yielded a narrow range of ages between >. 257. Ma and ~. 260. Ma. The new results are consistent with the estimates from magneto-biostratigraphic data and a rapid emplacement model. The new Wuchiapinqian ages of the Huangcao and Daheishan plutons suggests that magmatism may have lasted significantly less than 10. Ma as previously suggested, and the precise ages of the mafic dykes refute the hypothesis that Emeishan 'high-Ti' basalts represent the waning stages of the ELIP magmatism. The short duration of magmatism also implies that degassing of the host sediments (mostly carbonates), and thus releasing of greenhouse gasses occurred within a substantially shorter interval than previously thought, which significantly changes the loading of atmosphere per time unit. The latter corollary potentially has severe environmental effects that may have contributed to causing the end-Guadalupian mass extinction.