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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Asteroid/comet impact clusters, flood basalts and mass extinctions: Significance of isotopic age overlaps
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Asteroid/comet impact clusters, flood basalts and mass extinctions: Significance of isotopic age overlaps

机译：小行星/彗星撞击星团，玄武岩洪水和大灭绝：同位素年龄的意义重叠

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Morgan et al. [J. Phipps Morgan, T.J. Reston, C.R. Ranero. Earth Planet. Sci. Lett. 217 (2004) 263-284.], referring to an overlap between the isotopic ages of volcanic events and four epoch/stage extinction boundaries, suggest a dominant role of Continental Flood Basalts (CFB) and of explosive CO2-rich volcanic pipes ("Verneshots") as mass extinction triggers. Here I point out that Morgan et al. overlook 3 overlaps between the ages of extraterrestrial impacts, volcanic and mass extinction events, and 3 overlaps between the ages of extraterrestrial impact and volcanic events. These overlaps suggest that both extraterrestrial impacts and volcanism served as extinction triggers separately or in combination. A protracted impact cluster overlaps extinctions at the end-Devonian (similar to 374-359 Ma) and impact-extinction age overlaps occur in the end-Jurassic (similar to 145-142 Ma), Aptian (similar to 125-112 Ma); Cenomanian-Turonian (similar to 95-94 Ma); K-T boundary (similar to 65.5 Ma) and mid-Miocene (similar to 16 Ma) (Table 1). Morgan et al. appear to question the uniqueness of shock metamorphic and geochemical criteria used to identify asteroid/comet impacts. However, shock pressures at 8-35 GPa, indicated by intra-crystalline planar deformation features (PDF), exceed lithospheric and volcanic explosion pressures by an order of magnitude and are not known to be associated with explosive volcanic diatremes, kimberlites or lamproites. These authors make reference to apparent iridium anomalies of volcanic origin. However, platinum group element (PGE) abundance levels, volatile/refractory PGE ratios, and Cr and Os isotopes of meteoritic materials are clearly distinct from those of terrestrial volcanics. Given a Phanerozoic time-integrated oceanic/continent crustal ratio > 2.5 and the difficulty in identifying oceanic impacts, I suggest the effects of large impacts on thin thermally active oceanic crust-capable of triggering regional to global mafic volcanic events and ensuing environmental effects-provide an essential clue for understanding the relationships between impacts and volcanic events which, separately or in combination, result in deleterious environmental effects, in some instances leading to mass extinctions. (c) 2005 Elsevier B.V. All rights reserved.
机译：Morgan等。 [J.菲普斯·摩根（T.J.雷斯顿（C.R. Ranero）地球行星。科学来吧217（2004）263-284。]，指的是火山事件的同位素年龄与四个时代/阶段的灭绝边界之间的重叠，这表明大陆洪水玄武岩（CFB）和易爆的富含CO2的火山岩管道起着主导作用（ Verneshots“）作为大灭绝的触发。在这里，我指出Morgan等。忽略了地外影响，火山和大规模灭绝事件的年龄之间的3个重叠，以及地外影响与火山事件的年龄之间的3个重叠。这些重叠表明，地外影响和火山活动既是灭绝的诱因，又是两者结合的。延长的撞击群在德文纪末期与灭绝重叠（类似于374-359 Ma），而在侏罗纪末期（类似于145-142 Ma），阿普提安（类似于125-112 Ma），碰撞消灭年龄重叠。西诺曼尼亚-突尼斯（类似于95-94 Ma）; K-T边界（约65.5 Ma）和中新世中期（约16 Ma）（表1）。 Morgan等。似乎质疑用来识别小行星/彗星撞击的冲击变质和地球化学标准的独特性。但是，由晶体内平面变形特征（PDF）表示的8-35 GPa冲击压力超过了岩石圈和火山爆炸压力一个数量级，并且与爆炸性火山岩，金伯利岩或锂铁矿不相关。这些作者提到了火山起源的明显铱异常。但是，陨石材料的铂族元素（PGE）含量水平，挥发性/难熔PGE比率以及Cr和Os同位素与陆地火山明显不同。考虑到远生代时间积分的海洋/大陆地壳比率> 2.5以及识别海洋影响的难度，我建议大的影响对薄的热活动海洋地壳的影响，能够触发区域性到全球性的镁铁质火山事件，从而提供环境影响理解撞击和火山事件之间关系的基本线索，这些事件单独或结合在一起会导致有害的环境影响，在某些情况下会导致大灭绝。 （c）2005 Elsevier B.V.保留所有权利。

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