Precise age determination of mafic and felsic intrusive rocks from the Permian Emeishan large igneous province (SW China)
Precise age determination of mafic and felsic intrusive rocks from the Permian Emeishan large igneous province (SW China)
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DOI：
10.1016/j.gr.2011.10.009
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发表时间：
2012-07
影响因子：
6.1
通讯作者：
J. Shellnutt;S. Denyszyn;R. Mundil
中科院分区：
文献类型：
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作者：
J. Shellnutt;S. Denyszyn;R. Mundil
利用不同的（主要是微束分析）技术对峨眉山大火成岩省（ELIP）的岩石进行放射性同位素定年，得出了从Capitanian到早三叠世的年龄范围。相比之下，基于古生物学和古地磁资料的估计表明，ELIP的就位速度很快（≤2Ma），火山作用结束于~257Ma。通过对内蒙古攀西地区（内带）战略侵入岩进行CA-TIMS U-Pb年龄分析，获得了精度优于微束分析的锆石CA-TIMS U-Pb年龄。黄草（258.9±0.7Ma）、大黑山（259.1±0.5Ma）、水（259.6±0.5Ma）、西达（258.4±0.6Ma）正长花岗岩和3条基性岩脉（259.2±0.4Ma、259.5±0.8Ma、257.6±0.5Ma）的年龄范围在bb0 - 257Ma ~ ~260Ma之间。新的结果与磁生物地层资料和快速就位模型的估计一致。黄草和大黑山岩体的新五家品前年龄表明，岩浆活动可能持续时间明显少于10Ma，而镁质岩脉的精确年龄反驳了峨眉山“高钛”玄武岩代表ELIP岩浆活动衰落阶段的假设。岩浆活动持续时间短也意味着宿主沉积物（主要是碳酸盐）的脱气和温室气体的释放发生在比以前认为的短得多的时间间隔内，这显著改变了单位时间内大气的负荷。后一种推论可能对环境造成严重影响，可能是导致瓜德鲁普末期大灭绝的原因之一。
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 (≤2Ma) and that volcanism ended by ~257Ma. 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±0.7Ma), Daheishan (259.1±0.5Ma), Woshui (259.6±0.5Ma) and Cida (258.4±0.6Ma) syenitic and granitic plutons and three mafic dykes (259.2±0.4Ma; 259.5±0.8Ma, 257.6±0.5Ma) yielded a narrow range of ages between >257Ma and ~260Ma. 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 10Ma 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.