New constraints on the Paleoarchean meteorite bombardment of the Earth – Geochemistry and Re-Os isotope signatures of spherule layers in the BARB5 ICDP drill core from the Barberton Greenstone Belt, South Africa
New constraints on the Paleoarchean meteorite bombardment of the Earth – Geochemistry and Re-Os isotope signatures of spherule layers in the BARB5 ICDP drill core from the Barberton Greenstone Belt, South Africa
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古太古代陨石轰击地球的新限制 南非巴伯顿绿石带 BARB5 ICDP 钻芯中球体层的地球化学和铼锇同位素特征
DOI：
10.1016/j.gca.2017.05.040
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发表时间：
2017
影响因子：
5
通讯作者：
Reimold
中科院分区：
文献类型：
--
作者：
Schulz;Koeberl;Luguet;Van Acken;Mohr-Westheide;Oezdemir;Reimold
太古宙球粒层是由大型地外天体撞击产生的，迄今为止是早期陨石、小行星和彗星撞击地球的唯一遗迹。只有少数的太古代撞击碎片层被记录下来，所有这些碎片都嵌入了南非巴伯顿绿岩带（BGB）和西澳大利亚皮尔巴拉绿岩带（Pilbara）的32.3 - 34.7亿年的继承物中。其中一些可能相互关联。鉴于太古代球粒沉积物的稀缺性，本研究分析了最近从中央巴伯顿绿岩带回收的BARB 5岩心的四个球粒层交叉点，为获得早期陆地撞击轰击的新见解提供了机会。尽管被热液覆盖，来自BARB 5岩心的富含球粒样品的亲铁元素丰度特征，至少部分，留下了陨石指纹BARB 5球粒层的产生的影响假说支持的丰度之间的相关性适度（铬，钴，镍）和高度亲铁（Re，Os，Ir，Pt，Ru和Pd）的元素，其峰值浓度和元素间的比例范围内的那些为辉长岩。铼-锇同位素证据进一步支持撞击假说。总的来说，这项研究为四个分析的BARB 5球粒层中的三个提供了从100%到100%的地外混合物的证据，并为它们的成因提供了一个场景，涉及（i）陨石火流星撞击沉积目标，（ii）陨石成分与目标材料的不同混合物，（三）通过撞击蒸气羽流中的冷凝形成小球，（四）小球的运输和在海底条件下的沉积，然后是（五）过渡金属和高度亲铁元素在撞击后的适度再活动。
Archean spherule layers, resulting from impacts by large extraterrestrial objects, to date represent the only remnants of the early meteorite, asteroid, and comet bombardment of the Earth. Only few Archean impact debris layers have been documented, all of them embedded in the 3.23–3.47 billion year old successions of the Barberton Greenstone Belt (BGB) in South Africa and the Pilbara Craton in Western Australia. Some of them might be correlated with each other. Given the scarcity of Archean spherule deposits, four spherule layer intersections from the recently recovered BARB5 drill core from the central Barberton Greenstone Belt, analyzed in this study, provide an opportunity to gain new insight into the early terrestrial impact bombardment.Despite being hydrothermally overprinted, siderophile element abundance signatures of spherule-rich samples from the BARB5 drill core, at least in part, retained a meteoritic fingerprint. The impact hypothesis for the generation of the BARB5 spherule layers is supported by correlations between the abundances of moderately (Cr, Co, Ni) and highly siderophile (Re, Os, Ir, Pt, Ru and Pd) elements, whose peak concentrations and interelement ratios are within the range of those for chondrites. Rhenium-Osmium isotope evidence further support the impact hypothesis.Collectively, this study provides evidence for extraterrestrial admixtures ranging between ∼40 and up to 100% to three of the four analyzed BARB5 spherule layers, and a scenario for their genesis involving (i) impact of a chondritic bolide into a sedimentary target, (ii) varying admixtures of meteoritic components to target materials, (iii) spherule formation via condensation in an impact vapor plume, (iv) transportation of the spherules and sedimentation under submarine conditions, followed by (v) moderate post-impact remobilization of transition metals and highly siderophile elements.
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