Abstract in http://www.lpi.usra.edu/meetings/gold2001/pdf/3519.pd

Kennedy, AK

Malpas, JG

Robinson, PT

Song, XY

Sun, M

Thompson, G

Yan, DP

Zhang, CJ

Zhou, MF

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1SHRIMP zircon geochronology of the Emeishan Large Igneous Province (SW China): implications for doublemass extinctions in Late Permian M.-F. Zhou1, J. Malpas1, X.-Y. Song1, P. T. Robinson1, A. K. Kennedy1, M. Sun1,G. Thompson1, D.-P. Yan1, and C.-J. Zhang1:  1Department of Earth Sciences, University of Hong Kong, Hong Kong,China; 2Department of Applied Physics, Curtin University of Technology, Perth, Australia; 3Chendu University ofTechnology, Chengdu, ChinaIt is well documented that the Siberian Trapserupted at the end of the Permian at 251Ma 1,2.Eruption of the voluminous Emeishan flood basalts(EFB) in SW China was also previously thought to bethe source of the Permo-Triassic (P/T) boundaryvolcanic layer in the Meishan section, ZhejiangProvince, China3. The precise age dating of the EFBis thus important in the context of the relationship ofevents at the time of the Late Permian or P/Tboundary.The Emeishan Large Igneous Province isrepresented by voluminous flood basalts andsynchronous mafic intrusions which are considered asfeeders. The Emeishan volcanic succession covers anarea of more than 5x105 km2 with  thicknesses rangingfrom several hundred meters up to 5 km.  In thewestern part of the province, the volcanic successionwas strongly deformed, uplifted and eroded as aresult of the India-Eurasia collision.  Several N-Strending faults in the Yuanmiao-Xichuan region haveexposed Emeishan dykes over a considerable range ofcrystallization depths.  The feeders intrude variouslithologies in the region and are the hosts of major oredeposits, e.g., V-Ti-magnetite deposits and Ni-Cu-(PGE) sulfide deposits.  New SHRIMP zircon datingresults reveal that the igneous activity is older thanpreviously thought.  Two Ni-Cu-(PGE)-bearing,peridotite-gabbro intrusions, the Xinjie and Zhubuintrusions, have crystallization ages of 258.7 +/- 1.5Ma, and 256.0 +/- 1.0 Ma, respectively.  These newdates are consistent with observations that the basaltsare overlain by the Xuanwei Formation below the thePermo-Triassic (P/T) boundary layer.Stanley and Yang (1994)4 find two peaks inthe rates of extinction, one at the end of theGuadalupian (approximately 258 Ma), and another 8Ma later, at the end of the Tatarian, i.e., the Permo-Triassic boundary proper.  Holser and Magaritz(1987)5 had already pointed out two sharp minima ofsea level at these two times.  Based on their literaturereviews, Courtilllot et al. (1999)6 proposed that theEFB was erupted at the end of the Guadalupian,causing the earlier one of the two phases of massextinction. Our study provides the first directevidence of a temporal relationship between eruptionof the EFB and the mass extinction at 258 Ma andsupports the idea of a causal relationship.  Our resultsclearly rule out a temporal coincidence between theEFB and the mass extinction episode at the P/Tboundary and support the suggestion that there aretwo extinction events in Late Permian: one at the P/Tboundary and the other one slightly (about 5 to 8m.y.) earlier.REFERENCES:[1] Renne PR., et al., 1995, Science 269, 1413-1416;[2] Kamo SL., et al., 1996, Geochimica etCosmochimica Acta, 60, 3505-3511; [3] Chung SL.,and Jahn BM., 1995, Geology, v.23, 889-892; StanleySM., and X. Yang, 1994, Science 266, 1340-1344; [5]Holser WT., and Magaritz M., 1987, ModernGeology, 11, 155-180; [6] Courtillot V., et al., 1999,Earth and Planetary Science Letters, 166, 177-195.Eleventh Annual V. M. Goldschmidt Conference  (2001) 3519.pdf

SHRIMP zircon geochronology of the Emeishan Large Igneous Province (SW China): implications for double mass extinctions in Late Permian

http://www.lpi.usra.edu/meetings/gold2001/pdf/3519.pdf

SHRIMP zircon geochronology of the Emeishan Large Igneous Province (SW China): implications for double mass extinctions in Late Permian

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