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首页> 外文期刊>Geological Society of America Bulletin >An Early Ordovician Ar-40-Ar-39 age for the similar to 50 km Carswell impact structure, Canada
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An Early Ordovician Ar-40-Ar-39 age for the similar to 50 km Carswell impact structure, Canada

机译：早期ordovician AR-40-AR-39年龄类似于加拿大50 km Carswell影响结构的年龄

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摘要

The formation age of the large (similar to 50 km) Carswell impact structure, Canada, has been a matter of debate ever since its discovery five decades ago, with proposed ages ranging from Mesoproterozoic to Early Cretaceous. Here, we present new (ArAr)-Ar-40-Ar-39 data for aliquots of euhedral adularia, separated from vesicles in an impact melt rock from the central uplift of the structure. The analyses of the adularia yielded a statistically robust Early Ordovician crystallization age of 481.5 +/- 0.8 Ma (2s, mean square of weighted deviates = 1.06, P = 0.30). The most plausible explanation for the formation of vesicle-filling adularia is through low-temperature mineral precipitation during residual hydrothermal circulation that followed the impact, as no other known major intrusive, extrusive, or thermal events have occurred in the Carswell region in the Phanerozoic. The new age of the Carswell impact structure overlaps within uncertainty with the most precise Ar-Ar ages proposed for the L-chondrite parent body breakup event, but not with the age of the stratigraphic sequence from which the meteorites and micrometeorites from this event were recovered. Thus, either the Carswell impact represents a separate, unrelated impact event, or the dynamic evolution of the L-chondrite parent body breakup is more complicated than presently understood, and Carswell represents one of the earliest and largest known impacts of this event on Earth.
机译：加拿大的大型（类似于50公里）的组装年龄（类似于50公里），自200年前发现以来一直是辩论的问题，提出年龄从中蛋白古代到早期白垩纪。在这里，我们提出了新的（Arar）-AR-40-AR-39数据，用于等分试样的Euhedral Adularia，从结构的中央隆起中与冲击熔体岩体中的囊泡分开。 Adularia的分析产生了481.5 +/- 0.8 mA（2s，加权偏差= 1.06，P = 0.30）的统计学上强劲的早期orovician结晶年龄。最合理的解释囊泡填充性亚特区是通过低温矿物沉淀，在近撞击的残余水热循环期间，由于不在Phanerozoic的Carswell区域中没有发生其他已知的主要侵扰性，喷射或热事件。 Carswell冲击结构的新时代在不确定的不确定度与L-Chondrite父母身体分发事件提出的最精确的AR-AR，但没有与从该事件中的陨石和微晶体的地层序列的年龄恢复。因此，Carswell影响代表了单独的，无关的冲击事件，或者L-Chondrite父体分手的动态演变比现在更加复杂，并且Carswell代表该事件在地球上最早和最大的已知影响之一。

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