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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 >Absolute dating of the L-chondrite parent body breakup with high-precision U-Pb zircon geochronology from Ordovician limestone
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Absolute dating of the L-chondrite parent body breakup with high-precision U-Pb zircon geochronology from Ordovician limestone

机译：L-Chondrite父体身体分解的绝对约会，具有来自Ordovician石灰岩的高精度U-PB锆石地理学

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The breakup of the L-chondrite parent body (LCPB) in the mid-Ordovician is the largest documented asteroid breakup event during the past 3 Gyr. It affected Earth by a dramatic increase in the flux of L-chondritic material and left prominent traces in both meteorite and sedimentary records. A precise constraint on the timing of the LCPB breakup is important when evaluating the terrestrial biotic and climatic effects of the event, as well as for global stratigraphic correlations. Direct dating using heavily shocked L chondrites is hampered by both incomplete initial K-Ar degassing and isotopic resetting by later impact events. In order to better constrain the absolute age of this event we carried out high-precision U-Pb dating of zircons from three limestone beds recording discrete volcanic ash fallouts within mid-Ordovician strata in southern Sweden. These strata are rich in fossilized L-chondritic meteorites (1-20 cm large) that arrived on Earth shortly after the breakup event. Zircons from the ash-bearing layers provide stratigraphically consistent depositional ages that range from 464.22 +/- 0.37 Ma to 465.01 +/- 0.26 Ma. Combined with recently published 3 He profiles that pinpoint the arrival on Earth of the first dust from the breakup, and sedimentation rates constrained by cosmogenic Ne-21 in the fossil meteorites, the LCPB breakup is estimated to have occurred at 465.76 +/- 0.30 Ma. This provides the presently most precise absolute dating of the LCPB breakup, enabling a robust global stratigraphic correlation of bounding strata. Based on our new U-Pb data for the ash-bearing beds, the absolute ages for the boundaries of biozones and Dapingian-Floian stages overlap within error with those given by the 2012 Geological Timescale and require no modification. (C) 2020 Elsevier B.V. All rights reserved.
机译：中奥陶涅师的L-Chondrite父母身体（LCPB）的分解是过去3个Gyr期间最大的文档的小行星分手事件。它受到L-Chondritic材料的助焊剂的显着增加，并且在陨石和沉积记录中留下突出痕迹的剧烈增加。在评估事件的地面生物和气候效果以及全球地层相关性时，对LCPB分解的时间的精确约束很重要。通过不完全初始K-AR脱气和同位素复位，通过后来的影响事件阻碍了使用严重震惊的L Chondrites的直接约会。为了更好地限制了这一事件的绝对年龄，我们从三个石灰岩床上进行了高精度的U-PB约会，在瑞典南部的中奥陶器地层中记录了离散火山灰烬。这些地层富含僵化的L-Chondritic陨石（1-20厘米大），在分手事件后不久就到达了地球上。来自灰烬层的锆石提供了层层一致的沉积年龄，其范围为464.22 +/- 0.37 mA至465.01 +/- 0.26 mA。结合最近发表的3个他的档案，可以确定从分解的第一个粉尘的到达的档案，并且在化石陨石中由宇宙元素Ne-21限制的沉降率，估计LCPB分类在465.76 +/- 0.30 mA时发生。这提供了LCPB分解的目前最精确的绝对约会，从而实现了边界地层的稳健全球地层相关性。基于我们的灰烬床的新U-PB数据，生物区域和Dapingian-Floian阶段的边界的绝对年龄在2012年地质时间级或不需要修改时重叠。 （c）2020 Elsevier B.v.保留所有权利。

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