科研之友
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摘要
The hypothesis that the Permo-Triassic boundary (PTB) mass extinctions were caused by flood basalt volcanism in Russia (Siberian Traps) and/or China (the Emeishan Traps) is investigated from the point of view of time of occurrence (Ar-40/Ar-39 ages). Numerous published ages in the literature are rejected as good estimates of the time of crystallization. The filters applied in this respect are (a) statistical reliability of plateau/isochron sections of stepheating data and (b) the alteration state of the material that was dated. Alteration appears to be ubiquitous, unsurprising since most of the material dated was used without acid leaching - a procedure that is effective in yielding fresh(er) samples. Of similar to 70 ages in the literature for the main pulse of Siberian Trap volcanism, less than ten prove to be reliable ages. Similar techniques applied to Ar-40/Ar-39 for the Emeishan Traps, leaves only a single reliable age for the magmatic episode. These ages are compared to both published and new Ar-40/Ar-39 ages for the PTB as based on analysis of minerals' from critical ash beds in China. There is good overlap in the ages (PTB - 250.0 +/- 0.1 Ma, Siberian Trap lavas - 250.1 +/- 0.4 Ma), lending credence to a genetic link between the formation of the Siberian Traps and the faunal extinction event at the PTB. A similar link for the formation of the Viluy Traps (Russia) and the Late Devonian extinction event is investigated; only a single reliable Ar-40/Ar-39 age is available for the Viluy Traps, and falls close to the interpolated age for the Frasnian-Fammenian boundary. The use of the unspiked K-Ar technique to yield accurate ages for such (altered) samples is questioned. A review of U-Pb data pertinent to these problems suggests a close temporal link between the formation of the Siberian Traps and the PTB. Comparison of U-Pb and Ar-40/Ar-39 ages for the PTB, raises questions about the accuracy of high precision sanidine ages, possibly resulting from very slow leakage of Ar-40* from this mineral.
- 出版日期2014-4-15
